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JOURNAL 

OF THE SOCIETY OF 

MOTION PICTURE ENGINEERS 

Volume XXXV July, 1940 

CONTENTS 

Page 
Speed Up Your Lens Systems W. C. MILLER 3 

Progress in Projection Lighting W. C. KALB 17 

Gases from Carbon Arcs and Their Effects. . , .A. C. DOWNES 32 

Audience Noise as a Limitation to the Permissible Volume 
Range of Dialog in Sound Motion Pictures . . W. A. MUELLER 48 

Partial Deafness and Hearing- Aid Design . . . . W. B. BEASLEY 59 
Report of the Studio Lighting Committee 86 

New Motion Picture Apparatus 

New Lenses for Projecting Motion Pictures. . W. B. RAYTON 89 

Current Literature 98 

1940 Fall Convention at Hollywood, Calif., October 2 lst-25th, 
inclusive 100 

Society Announcements 105 



JOURNAL 

OF THE SOCIETY OF 

MOTION PICTURE ENGINEERS 



SYLVAN HARRIS, EDITOR 

Board of Editors 
J. I. CRABTREE, Chairman 

A. N. GOLDSMITH A. C. HARDY T. E. SHEA 

J. G. FRAYNB L. A. JONES G. E. MATTHEWS 

E. W. KELLOGG 



Subscription to non-members, $8.00 per annum ; to members, $5.00 per annum, 
included in their annual membership dues; single copies, $1.00. A discount 
on subscription or single copies of 15 per cent is allowed to accredited agencies. 
Order from the Society of Motion Picture Engineers, Inc., 20th and Northampton 
Sts., Easton, Pa., or Hotel Pennsylvania, New York, N. Y. 
Published monthly at Easton, Pa., by the Society of Motion Picture Engineers. 

Publication Office, 20th & Northampton Sts., Easton, Pa. 
General and Editorial Office, Hotel Pennsylvania, New York, N. Y. 

West Coast Office, Suite 226, Equitable Bldg., Hollywood, Calif. 
Entered as second class matter January 15, 1930, at the Post Office at Easton, 
Pa., under the Act of March 3, 1879. Copyrighted, 1940, by the Society of 
Motion Picture Engineers, Inc. 

Papers appearing in this Journal may be reprinted, abstracted, or abridged 
provided credit is given to the Journal of the Society of Motion Picture Engineers 
and to the author, or authors, of the papers in question. Exact reference as to 
the volume, number, and page of the Journal must be given. The Society is not 
responsible for statements made by authors. 



OFFICERS OF THE SOCIETY 

* President: E. A. WILLIFORD, 30 East 42nd St., New York, N. Y. 

* Past-President: S. K. WOLF, RKO Building, New York, N. Y. 

* Executive Vice-President: N. LEVINSON, Burbank, Calif. 

** Engineering Vice-President: D. E. HYNDMAN, 350 Madison Ave., New York, 
N. Y. 

* Editorial Vice-President: J. I. CRABTREE, Kodak Park, Rochester, N. Y. 

** Financial Vice-President: A. S. DICKINSON, 28 W. 44th St., New York, N. Y. 

* Convention Vice-President: W. C. KUNZMANN, Box 6087, Cleveland, Ohio. 

* Secretary: J. FRANK. JR., 356 W. 44th St., New York, N. Y. 

* Treasurer: R. O. STROCK, 3511 35th St., Astoria, Long Island, N. Y. 

GOVERNORS 

* M. C. BATSEL, Front and Market Sts., Camden, N. J. 

* J. A. DUBRAY, 1801 Larchmont Ave., Chicago, 111. 
** A. N. GOLDSMITH, 580 Fifth Ave., New York, N. Y. 
** H. GRIFFIN, 90 Gold St., New York, N. Y. 

* P. J. LARSEN, 29 S. Munn Ave., East Orange, N. J. 

* L. L. RYDER, 5451 Marathon St., Hollywood, Calif. 

** A. C. HARDY, Massachusetts Institute of Technology, Cambridge, Mass. 

* H. G. TASKER, 5451 Marathon St., Hollywood, Calif. 

* Term expires December 31, 1940. 
** Term expires December 31, 1941. 



SPEED UP YOUR LENS SYSTEMS' 
WILLIAM C. MILLER** 



Summary. The tendency of bare glass surfaces to reflect light has always pre- 
sented a serious problem in optics. New discoveries in the field of physics have re- 
sulted in methods of reducing these light reflections. One of these methods has proved 
practicable for general use in optical equipment. The reduction of reflections in 
treated systems has been so great that ghosts and flares are rarely encountered. The 
light no longer reflected by the glass surfaces is transmitted by the optical systems, in- 
creasing their efficiency. Camera lenses treated with the new process show an increase 
in speed of nearly a full stop. New applications of the process are being found almost 
daily. 

At times the reflectivity of the polished surface of optical glass may 
have its uses. More often, however, the applications of optical 
glass are of such a nature that the surface reflection is a decided dis- 
advantage. It reduces the efficiency of optical systems by robbing 
the transmitted beam at every air-glass surface. Furthermore, the 
light thus subtracted from the primary beam may appear again in 
the form of flares where it is not wanted. For example: in a modern 
photographic lens at every air-glass surface from 4 to 6 per cent of the 
incident light is reflected and the transmitted beam is correspondingly 
reduced in intensity. After passing several surfaces, say, 8, as in 
the case of the Astro Pan Tachar, B altar, and Cooke Speed Panchro 
lenses, the transmitted beam has been reduced to about 64 per cent 
of the original intensity. The greater the number of air-glass sur- 
faces in a system and the higher the average index of refraction of the 
elements, the greater is this loss. Fig. 1 shows the losses suffered in 
various lens systems in terms of the number of air-glass surfaces. 

About 50 years ago H. Dennis Taylor observed that certain optical 
glasses acquired a tarnish after prolonged exposure to the air. This 
tarnish was in the form of a colored film. Becoming interested in 
these surfaces, Taylor made measurements on them, and found that 
this tarnish was not reducing the light transmission of the lens but on 

* Presented at the 1940 Spring Meeting at Atlantic City, N. J.; received 
April 19, 1940. 

** Paramount Pictures, Inc., Hollywood, Calif. 

3 



W. C. MILLER 



[J. S. M. P. E. 



the contrary was increasing it by reducing the amount of reflection 
from the affected surfaces. This phenomenon and its potentialities 
so intrigued Taylor that he began a series of tests to determine 
whether the tarnish could be stimulated artificially by chemical 
means. His work was only partially successful. The number of 
kinds of glass which he could treat was very limited and the reduction 
in reflectivity which he obtained was not sufficiently great to prove 
of practical value. 



2 

r 

20 



UNTREATED SYSTEMS 



6 8 10 12 

NUMBER OF AIR-GLASS SURFACES 



FIG. 1. The light transmission of optical systems in terms of the number 
of air-glass surfaces involved. A simple magnifying glass having two surfaces 
transmits about 90 per cent of the incident light. Common camera lenses 
having six surfaces transmit, on the average, about 73% of the incident light 
exclusive of that lost by absorption. This curve is computed for systems 
having an average reflectivity of 5 per cent at each air-glass surface. For 
systems having a higher average reflectivity, the losses would be greater, and 
vice versa. 

The idea did not die at that point, however, for others took up this 
work. Most notable among these experimenters were Kollmorgen, 
Kellner, Wright, and Ferguson. By them the chemical method has 
been brought to a point where it now has practical value. Certain 
glasses, notably the dense lead flints, can be treated with a nitric 
acid bath and the surface etched in such a manner that reflections 
are reduced without producing scattering of the transmitted beam. 
The chemical treatment dissolves out minute particles of the lead 
oxide lying near the surface of the glass. The removal of this ma- 
terial results in the formation of tiny cavities. The treatment is 



July, 1940] SPEED UP YOUR LENS SYSTEMS 5 

carried on until the etching has penetrated to a prescribed depth. 
When the lens is dried, air penetrates these cavities, whose dimen- 
sions are smaller than a wavelength of light and, therefore, produce 
no scattering effect upon the incident light. The result of the pene- 
tration of the air into the surface of the glass is that the average index 
of refraction of the surface layer is reduced. A light-ray incident 
upon such a treated surface encounters this thin layer of material of 
low index, with the result that reflection is reduced. However, the 
proportions of air to glass in the etched layer can not be made great 
enough to produce the maximum effect and the reduction of re- 
flections is not as great as one might expect was physically possible. 

There are three reasons why the chemical method has not been 
widely applied. First, the reduction of reflections by the chemically 
treated surface is low; second, the types of glass that can be treated 
are limited; and third, the process can get out of control and ruin 
expensive optical elements. 

Realizing the seriousness of these limitations, Dr. John Strong, of 
the California Institute of Technology, began an investigation of this 
phenomenon in 1935. 1 It was his aim to find a method that would 
be more effective in reducing the reflections from glass surfaces and 
would be independent of the chemical nature of the surface upon 
which it was to be applied. Also, it was his aim to find a process 
whose effect could be removed when desired, leaving the glass in its 
original condition. This aim was achieved by a physical rather than 
a chemical treatment of the surface. 

Dr. Strong pointed out on theoretical grounds that a film 1 /4 wave- 
length in thickness deposited on the glass surface will produce the 
maximum effect on the amount of light reflected. Furthermore he 
showed that if the index of refraction of the deposited film were equal 
to the square-root of the index of refraction of the glass upon which it 
lies the intensity of the normally reflected light would be zero. The 
light not reflected by the treated surface is transmitted. However, 
for ordinary glasses the film must consist of a material having an index 
of about 1.25, a value less than that of any stable solid substance. 
Allowing certain compromises in the hardness and durability of the 
film, he was able to approximate that index closely enough to elimi- 
nate 85 per cent of the surface reflection. 

This low index of refraction was obtained in a novel way. A film 
of suitable material was deposited on a glass surface by the high- 
vacuum evaporation technic. He discovered that the film could be 



6 W. C. MILLER [J. S. M. P. E. 

deposited in a porous form so that air was able to penetrate it. Thus 
the film exhibited an index which was an average of the index of the 
evaporated material and that of the included air. By controlling the 
factors involved in the evaporation of the film he was able to get an 
index very nearly equal to the square-root of the index of the glass. 
The success of Dr. Strong's experiments is attested by the fact that 
he succeeded in reducing the reflectivity of plate-glass from 4 to 
0.6 per cent. For plates treated on both surfaces this corresponded 
to increasing the transmission from 92 to 99 per cent. 

Subsequently, Dr. Katherine Blodgett, 2 of the General Electric 
Laboratory, found another and quite different physical means of 
achieving the same results. She found that by dipping glass 46 times 
into a water bath covered with a monomolecular film of cadmium 
arachidate and arachidic acid, a film of the required thickness was 
built up on the glass. This film has too high an index in its original 
form, but by washing it in hot acetone Miss Blodgett reduced the 
index to the proper value. This treatment with acetone dissolved 
out the minute globules of arachidic acid, leaving a porous film of 
cadmium arachidate which, with the included air, have exactly the 
required index. 

Films obtained by Miss Blodgett's original process are exceedingly 
delicate and can therefore be used only on the most protected sur- 
faces. They will not stand heat and can not be cleaned or touched 
in any way. Furthermore, after having been washed with acetone, 
the films are so completely relieved of all grease that they have a 
great affinity for any oils that come in contact with them. Many 
dust particles that float in the air are laden with oils and greases. 
When such a fleck falls upon a cadmium arachidate-treated surface 
the film absorbs the oils from the dust, with the result that a small 
surrounding area changes its refractive index and loses its efficiency. 
As dust accumulates, therefore, the treated surface develops a large 
number of small glossy spots which have returned to the original 
index of the untreated glass. 

In all three processes described, the low-index surface layer must 
be J /4 of a wavelength in thickness to reduce the reflection of light of 
that particular color. Since the films obviously can not be 1 /4 wave- 
length thick for all wavelengths at once, the reduction of reflectivity 
must be a maximum for one color and less for others. In practice 
this color differential is not serious. Certain steps can be taken to re- 
duce it materially in photographic lenses in the few cases where an 



July, 1940] 



SPEED UP YOUR LENS SYSTEMS 



excess of a few per cent of one color in the transmitted beam is un- 
desirable. 

Comparison of the two physical methods, the one by Dr. Strong 
and the other by Miss Blodgett, shows that at the present time the 
one discovered by Dr. Strong is the most promising for general use. 
In view of this it has attracted the attention of several workers; 
notable among them are Cartwright 3 ' 4 and Turner, 3 who experi- 
mented with various materials, some of which offer certain advan- 
tages. 



200 
190 
ISO 
I 70 
160 
150 
140 
130 
120 
I 10 
100 



i 



i 



6 10 12 

NUMBER OF SURFACES 



FIG. 2. The light- transmission ratio of treated to untreated systems in 
terms of the number of air- glass surfaces involved. This curve represents 
the gains which can be realized by treatment of systems normally reflecting 
an average of 4 per cent at each air-glass surface. Several examples are 
noted on the graph of common optical systems composed of the indicated 
number of surfaces. 



A film deposited in a manner which will give the greatest possible 
reduction to reflections is so porous and soft that it has little mechani- 
cal strength. But by a compromise whereby one sacrifices some 
efficiency, increased durability is obtained. The resulting films are 
much more valuable for practical applications. The compromise 
films still effect reductions of 75 per cent in the reflectivity of glass 
surfaces and exhibit properties which are particularly well balanced 
for general use. 

At the request of Paramount Pictures, Dr. Strong treated a 3 -inch 
Astro Pan Tachar lens with which the first tests were made to deter- 



8 W. C. MILLER [J. S. M. P. E. 

mine the value and practicability of the process for motion picture 
work. These tests consisted of optical bench measurements and 
photographs of scenes made under severe production conditions. 
The results of the tests were so remarkable that a full set of camera 
lenses and several projection lenses were treated by Dr. Strong's 
process and placed in production. Further tests were made under 
very adverse conditions to determine just what new possibilities the 
treated lenses presented. 

Photometric measurements show that treated lenses transmit 
about 40 per cent more light than identical untreated lenses. Refer- 
ence to Fig. 2 shows that this measured value compares favorably 
with the gain for an eight-surface system predicted from theoretical 
considerations. 

Photographic results obtained on a production set, however, 
indicate that the effective speed of the treated lenses has been in- 
creased by a larger amount than that indicated by photometric mea- 
surements. For example, the experience has been that scenes shot 
with the treated lenses printed between 4 and 6 Cinex printer-lights 
lower than the identical scenes made with untreated lenses. An 
average difference of 5.3 printer-lights indicates an increase of 58 
per cent in transmission. This apparent discrepancy is probably due 
to the difference in the methods of judging relative density in the 
two cases. It is also felt that the type of scene being photographed 
has some effect upon the apparent speed difference between treated 
and untreated lenses. Much more data than are now available must 
be studied to determine accurately the true effect of this treatment 
upon photographic speed. 

Optical bench tests show that the definition and resolving power 
of treated lenses are increased. There is also a very noticeable im- 
provement in image contrast and brilliance. The color correction of 
the lens is unchanged since this characteristic depends upon factors 
in no way affected by this treatment. 

The depth of focus at a given aperture is not changed since depth 
of focus depends entirely upon the linear aperture of the lens, which 
dimension is unaltered by the treatment. However, since the light 
transmission of a treated lens is increased at fixed light levels on a 
scene, the lens can be correspondingly stopped down. This reduction 
of aperture will add to the depth of focus of the treated lens. 

Reducing the reflectivity of the glass surfaces of the lens reduces 
the diffused light normally reaching the photographic film. This re- 



July, 1940) 



SPEED UP YOUR LENS SYSTEMS 




75 



?* no 




FIG. 3 (Upper). Photograph of a pencil drawing made with an un- 
treated lens. 

FIG. 4 (Lower). Photograph of the same drawing under identical 
conditions made with a treated lens. Notice the increased contrast and 
strength of the reproduction compared to that shown in Fig. 3. 



10 W. C. MILLER [J. S. M. P. E. 

suits in a surprising increase in the clarity with which low-key scenes 
are reproduced. The halftone reproductions accompanying this 
article illustrate the effects obtained, although the original photo- 
graphs exhibit these effects more clearly than do these reproductions. 
Although the benefits of treated lenses are particularly noticeable 
in low-key scenes due to low light-levels, they are also highly beneficial 
in ordinary photography. As an example, consider the application 




FIG. 5. The same subject as shown in Fig. 6, photo- 
graphed with a treated Astro Pan Tachar lens, showing 
its freedom from flares. In the original negative there 
was one faint flare still visible which has been lost in the 
process of reproduction, which is responsible, also, for 
the increased size of the halo around the sun's image in 
this picture. It was actually no larger with the treated 
lens than with the untreated one. 



of treated lenses for copying work. Anyone who has endeavored to 
copy a pencil drawing in black and white will be interested in com- 
paring Figs. 3 and 4, one made with a treated lens and the other with 
an identical untreated lens. The increased contrast with which this 
type of subject is rendered is a splendid example of the advantages 
offered by treated optics. Other types of copying are similarly 
facilitated by treatment. 

Internal reflections are responsible for the flares and ghosts so 
frequently encountered in photographic work. These flares are pro- 



July, 1940] SPEED UP YOUR LENS SYSTEMS 11 

duced by light originating from a bright object being reflected from 
one surface of a lens element and then being redirected by second re- 
flection toward the photographic film. Flares are strong when the 
reflecting lens surfaces have curvatures such that the redirected rays 
reach the film as a concentrated beam of light. By reducing the re- 
flectivity of the surfaces of the lens elements to V* of their original 
value, a beam reaching the film after two reflections will be weakened 




FIG. 6. An example of the lens flares obtained by 
shooting into the sun with an untreated Astro Pan 
Tachar lens. These flares are due to the inter-reflection 
of light-rays between the elements of the lens. The 
black line going through the sun is a distant cable pur- 
posely silhouetted to supply an object for comparison 
in this scene. 



16-fold. The intensity of the flare beam after four reflections from 
treated surfaces three being an impossible condition is reduced in 
intensity 256-fold. 

Figs. 5 and 6 show the results obtained by photographing directly 
into the sun with two identical lenses, one treated and one not. In 
the former instance, there is only one very faint flare, while with the 
latter there are thirteen strong ones in the original negative. If this 
freedom from flares can be accomplished with the sun as a source, it 
goes without saying that little trouble will be encountered from street 



12 W. C. MILLER IJ. S. M. P. E. 

lights, automobile headlights, bright windows, or artificial lights in 
rooms. 

Glass diffusion disks and filters are frequently the source of flares 
and ghosts. Treatment of their surfaces with a soft coating would 
cause occasional trouble due to the difficulty of keeping these films 
free from blemishes. Located, as they often are, some distance from 




FIG. 7. Photograph made with an untreated lens at 
very low light levels with an untreated f/2.3 Astro Pan 
Tachar lens. The light-intensity was purposely lowered 
to a point where satisfactory results could not be ob- 
tained with normal lenses of that speed. Compare the 
quality with that of Fig. 8, made with an identical 
treated lens with all lighting conditions remaining the 



the optical center of the camera lens, such blemishes would endanger 
the quality of the picture. To provide for the treatment of such 
surfaces as well as for the outside surfaces of lenses subjected to severe 
treatment, Dr. Strong has developed a method of applying a much 
harder and more durable film. Although the efficiency of this tough- 
ened film is less than that of the softer coating, it is still effective in 
reducing reflected light. Diffusion disks in use at Paramount, treated 
with the harder coat, show a reduction of reflections of 40 per cent 
per surface. 



July, 1940] 



SPEED UP YOUR LENS SYSTEMS 



13 



As an illustration of the increased definition and contrast obtained 
with treated lenses, cameramen find it necessary to use stronger dif- 
fusion. Unquestionably part of this effect is due to the reduction of 
scattered light which previously gave a false impression of diffusion. 
Now, however, with treated systems more nearly true diffusion will 
be realized. 

Gains made possible by treating camera lenses can also be realized 
with projection systems. A most promising application of the process 




FIG. 8. The same subject as shown in Fig. 7, photo- 
graphed under identical conditions with a treated Astro 
lens at the same aperture as that used for Fig. 7. Notice 
the increased brightness of the scene and the improved 
quality and definition obtained with the treated lens. 

is the treatment of projection lenses used in process photography. 
Here the need for more light is constantly felt. With the treatment 
applied to some of the modern eight-surface projection lenses, needed 
increases in screen illumination will be obtained without the sacrifice 
of image quality normally associated with increased optical speed. 
Recent tests made at the Paramount Studio show an increase of 50 
per cent in the screen brightness when treated projection lenses were 
used. This gain appears higher than that indicated in Fig. 2 for an 
eight-surface system, because the losses by reflection in that parti- 



14 W. C. MILLER [J. S. M. P. E. 

cular make of lens are unusually high due to the presence of elements 
having a high index of refraction and several highly curved surfaces. 

It is certainly interesting to note that by this relatively simple 
treatment, screen illumination has been increased 50 per cent at one 
jump, while in the past much time and money have been expended 
to achieve far smaller gains. 

Due to the many steps involved in producing a finished process 
shot, it is only with great care that good quality is maintained in the 
projected portion of the finished picture. The gains in definition and 
brilliance of the image obtained with treated lenses will greatly fa- 
cilitate this method of photography and add to the quality and scope 
of the art. 

This treatment would also appear to present advantages in sound 
recording where light transmission, definition, and contrast of image 
are vital At the present time several groups are experimenting 
with treated sound recording lenses. However, no information is 
yet at hand concerning the results obtained. Undoubtedly interesting 
reports will be forthcoming in the near future. 

Although the material presented so far in this paper has to do 
largely with the application of Dr. Strong's process to photographic 
objectives, in reality this is only one division of the field of possible 
applications. Visual instruments, such as binoculars and micro- 
scopes, give striking evidence of the practical use to which this treat- 
ment can be put. 

In the case of both binoculars and microscopes, the only aid which 
these instruments offer to normal vision is magnification. No instru- 
ment can increase the intrinsic brightness of an extended object or 
increase the contrast. But, owing to the losses by absorption in the 
glass and by reflection of light at the glass surfaces, such instruments 
reduce the brightness of an object and greatly detract from the con- 
trast and brilliance of the field. The excellence of certain makes of 
binoculars depends largely on clever design managed so that the 
effects of reflection are minimized. Moderately priced binoculars with 
treated surfaces will frequently be found to give better aid to vision 
than more expensive untreated instruments. Light transmission 
in treated glasses is greatly increased, as can be seen by reference to 
Fig. 2. At the same time, the contrast is increased through the elimi- 
nation of light scattered throughout the system. 

This new technic of reducing the reflection of glass surfaces prom- 
ises to come nearer to revolutionizing the uses and applications of 



July, 1940] SPEED UP YOUR LENS SYSTEMS 15 

optical glass than any other developments of the past several decades. 
Now for the first time it is possible to increase the speed of optical in- 
struments and photographic lenses and improve image quality simul- 
taneously. 

Although the process is in its infancy, the widespread interest 
which it has already aroused indicates the pressing need for the 
improvements that the treatment makes possible and the eager wel- 
come which it will receive from all those who depend upon optical 
equipment either for profit or pleasure. 



REFERENCES 

1 STRONG, J.: J. Opt, Soc. Amer., 26 (Jan., 1936), p. 73. 

2 BLODGETT, K. B. : Phys. Rev., 55 (April, 1939), p. 391. 

3 CARTWRIGHT, C. H., AND TURNER, A. F.: Phys. Rev., 55 (1939), p. 595(4). 

4 CARTWRIGHT, C. H.: /. Opt. Soc. Amer., 30 (Feb., 1940), p. 110. 



DISCUSSION 

MR. KURLANDER: How much farther could the lens be stopped down, also 
taking into account the reduction in lens flare? 

DR. RAYTON: There are two factors involved. One is an increase in light 
transmission, with respect to which I feel fairly familiar. There is another factor, 
referred to in Mr. Miller's paper, concerning which I feel incapable of reaching 
any opinion on a quantitative basis. 

I would like to express my pleasure at this paper that Mr. Miller has prepared. 
He has done an excellent job of laying this situation before you. I think his 
figures for gain in transmission are certainly top figures. I had the pleasure of 
speaking with Mr. Miller recently, when he referred to the projection lens that 
he had found to yield a 50-per cent increase in transmission. We had a little 
friendly disagreement as to whether or not that was possible. He could say only 
that his measurements indicated that, and I could only say that I found it a little 
difficult on theoretical grounds to see how it could reach that high figure. The 
matter was left there. Perhaps it is not greatly important. I think that in 
general his figures are justifiable, and that an increase in the light transmission 
of a photographic lens with eight surfaces of 35 per cent or that order is perfectly 
possible. 

The stops in a photographic lens are usually arranged so that the difference 
in exposure is 2 to 1 as we pass from one stop to the next, so that on the basis of 
increased transmission, the amount of stopping down that one can expect is 
something less than half a stop. 

In the American Cinematographer for March, 1940, Mr. W. Stull claimed that 
it was possible to reduce the aperture by one full stop in a lens with treated sur- 
faces. The explanation was based on some factors in addition to simple increase 
in transmission. 



16 W. C. MILLER 

Mr. Miller touched upon several other very interesting points that, if developed, 
could run the discussion on endlessly. There is the possibility of extending 
this treatment to other types of optical instruments. It has a fascinating future, 
but I do not think it is necessarily going to cure all the difficulties or reduce all 
the problems of the lens designer. 

DR. JONES: I think the thing Dr. Rayton has been driving at is, perhaps, a 
little further discussion on the effects of what we call flare light on picture quality; 
and by that I mean light which is uniformly distributed over the surface of the 
negative material. We must distinguish between that and the thing we call 
flare spots. Undoubtedly, this treatment is extremely efficient in eliminating 
these undesirable flare spots. 

When you go into the effect of flare light distributed over the surface of the 
materials, quite uniformly in many cases, the problem becomes quite compli- 
cated because we can not give a general solution and state exactly what will happen 
in all cases. 

Flare light is not all due to reflection from the lens surface. In any optical 
system, such as a camera, there are the lens, the diaphragm blades, shutter blades, 
in many cases, and, in the case of hand cameras, bellows. There is the barrel 
in which the lens is mounted. All these contribute somewhat to the magnitude 
of the flare light. So, as I see it, the complete elimination of reflections from the 
lens surfaces would not, in general, completely eliminate flare. 

Moreover, the amount of flare on the photographic surface will depend upon 
the characteristic of the scene being photographed; and upon the light distribu- 
tion of the entire field to which the lens of the camera is subjected. Of course, 
it is common practice to use lens hoods. Those hoods reduce the flare light, be- 
cause they protect the lens from a large portion of the peripheral field. 

As I said before, there is no general solution of the flare problem. It must be 
based upon specific conditions the entire optical system and what is out in 
front of it. A quantitative evaluation of what good will result from this method 
would have to be based upon a statistical study of a large number of scenes. 

Always, we must consider, to some extent, the influence of this flare light, or 
its absence, upon the quality of the final picture; and the only way I know to do 
that, other than by making practical tests, is to apply the tone reproduction 
analysis. 

MR. EDWARDS: There is one other condition. In the Super-Simplex, at 
least the later models, and in the E-7, the light goes through not only the lens, 
but also a very thin wafer of Pyrex glass situated in front of the aperture. If it 
is possible by the corrosion or etching method to save 2 or 3 per cent on each sur- 
face, etching this glass would give us a total of 5 or 6 per cent gain in light trans- 
mission. 

DR. GAGE : If the hard coating can be successfully applied to the thin wafer 
or to the condenser lenses, and so much dirt does not get onto them that frequent 
scrubbing is necessary so that the coating is worn off, it would be advantageous 
in letting more light through. 

Treating any of the condenser elements before the light strikes the film would 
give a slight increase in light. When we get to the objectives, the additional flare 
due to multiple reflections has a great deal more to do with the quality of the 
picture, so that it is doubly important to treat the objective. 



PROGRESS IN PROJECTION LIGHTING* 
W. C. KALB** 

Summary. The carbon arc has had an important part in the progress of the 
motion picture industry from the time of its origin to the present day. This narrative 
of the various improvements and developments which have kept the carbon arc in its 
preferred position as a source of projection light is presented in chronological sequence. 
Data are given relative to the progress made along five lines of improvement: intrinsic 
brilliancy of the crater, quality of light produced, volume of light on the screen, efficiency 
of light production, and economy of operation. 

Three physical properties of a widely distributed element lie at 
the very foundation of the motion picture industry and have had 
much to do with its remarkable record of progress. This element is 
carbon. The properties which are so vital to this industry are : good 
electrical conductivity, the fact that carbon does not melt, and the 
further fact that it can be raised to a temperature of more than 
3600C before changing from the solid to the vapor form. These 
physical properties permit small rods of carbon to be used as the ter- 
minal electrodes of the electric arc producing a light which rivals, in 
brilliancy and whiteness, the light of the sun itself. When Sir 
Humphry Davy in his classic experiment early in the 19th century 
produced the first electric arc between carbon electrodes he could 
have had no thought of the importance his discovery was to have in 
the development of an industry to be founded almost a century later. 
Yet the phenomenal strides made by the motion picture industry in 
its relatively few years of existence were made possible by the adapta- 
bility of the carbon arc to its expanding needs. 

Many other factors, including technical advances in other lines, 
have had important parts in the development of the motion picture 
industry over a relatively short span of years into one of the major 
industries of the country. The artistry of directors, cameramen, and 
actors have played a large part. The sagacity and courage of the 

* Presented at the 1940 Spring Meeting at Atlantic City, N. J. ; received May 
21, 1940. 

** National Carbon Co., Cleveland, Ohio. 

17 



18 W. C. KALB [J. s. M. P. E. 

industry's executives have contributed largely to its record of progress. 
These factors involving personalities have been given much publicity 
and have tended to overshadow the improvements in the carbon arc 
and its utilization which have likewise had a vital part in making 
possible the tremendous growth that has been realized. 

The optics of motion picture projection are such that a light-source 
of small dimensions and very high intrinsic brilliancy is essential. 
No light-source has been available throughout the history of the 
industry which satisfies these requirements so well as the carbon 
arc. The crater of the positive carbon offers an essentially flat field 
of light emission, sufficiently uniform in brilliancy over its entire 
area to provide a satisfactory uniformity of illumination on the 
largest screen. Due, however, to the enormous difference in area 
between the screen and the source of projection light, and to losses en- 
countered in the optical system, the brilliancy of the light-source 
must be millions of times that of the light reflected from the screen. 
It is therefore but natural that, from the first commercial exploitation 
of motion pictures, the carbon arc should have been selected as the 
source of projection light. For the carbon arc, at that time to be 
seen on almost every street corner, was by far the most brilliant 
source of light man had then produced. Subsequent improvements, 
the product of constant laboratory research, have kept the arc 
abreast of the needs of this growing industry. 

The first projection lamps burned the carbons in a position slightly 
inclined from the vertical, with the positive carbon in the upper 
position so that the brilliant positive crater was turned partially 
toward the condenser lens which focuses the light on the film aperture. 
Further exposure of the positive crater to the condenser lens was ac- 
complished in this type of lamp by adjusting the position of the 
negative carbon so that the tip of the positive carbon burns off on one 
side. From the first adaptation of the arc to projection there has 
been steady progress toward more and more efficient production and 
utilization of projection light. Developments in projector carbon 
manufacture have adapted the arc to more efficient optical systems 
and, combined with improvements in the lamps themselves, have 
successfully met the increasingly critical attitude of theater patrons 
and kept the carbon arc in its preferred position as a source of pro- 
jection light. 

The need for more light, first to increase the brightness of the 
screen image, and then to meet the needs of larger theaters, resulted 



July, 1940] 



PROGRESS IN PROJECTION LIGHTING 



19 



in the use of larger carbons and higher arc currents. Steadiness of the 
light was improved, first by making the positive carbon in the form 
of a thick-walled tube with a central core of softer, neutral carbon. 
This is done by extruding the plastic carbon mix from a huge hy- 
draulic press leaving a central opening in the carbon as may be seen 
in Fig. 1. After these "green" carbons have been baked and cut to 
length, the central opening is filled with core material in an auto- 
matic coring machine. Further improvement in steadiness of the 
arc was effected by using a metal-coated negative carbon, consider- 




FIG. 1. End of "green" carbon showing cen- 
tral opening for core. 

ably smaller in diameter than the positive. Fig. 2 is a drawing of this 
improved trim which indicates also the form of the positive crater. 
These improvements in the carbon trim, combined with improve- 
ments in optical systems, substantially increased the efficiency of the 
types of projection lamps then universally used. 

By this time motion picture theaters were getting away from the 
limitations to capacity which the audible range of voices from the 
stage had previously imposed on the theater. Houses seating 3000 
and 4000 patrons were being built, screens were enlarged for the 
benefit of the patrons in the rear seats, and the need for still more 
screen light became urgent. Fortunately, a new principle upon which 
the carbon arc could be operated was discovered at about this time. 



20 



W. C. KALB 



[J. vS. M. P. E. 



This has been aptly termed the "high-intensity" arc and, for dis- 
tinction, the term "low-intensity" arc has been applied to types of 
carbon arcs previously in use. 

The low-intensity, neutral cored carbon arc is seldom operated at 
a current-density much over 200 amperes per square-inch in the posi- 
tive carbon. The light used in projection all comes from the in- 
candescent crater face of the positive carbon, the brilliancy of which 
is determined by its temperature. Since carbon vaporizes at a tem- 
perature of about 3675C, further increase in current beyond the 

value which produces this temperature 
does not increase the crater tempera- 
ture and brilliancy but serves only to 
consume the carbon more rapidly. The 
philosophy is the same as that of the 
three-minute egg. You can turn up the 
gas and boil the water away more 
rapidly, but the temperature remains 
at 212F in the pan and the three- 
minute egg is still a three-minute egg. 
In practical operation the upper limit 
of crater brilliancy in the low-intensity, 
d-c arc is approximately 175 cp per 
sq-mm. 

In the high-intensity arc the core of 
the positive carbon is relatively larger 
than in the low-intensity arc and con- 
tains certain rare-earth materials which 
become highly luminescent under the 
action of the electronic bombardment 




CORED 
POSITIVE 
CARBON 



CRATER 



OROTIP 

NEGATIVE 

CARBON 



FIG. 2. Drawing of car- 
bon trim for d-c low-in- 
tensity condenser - type 
lamp. 



in the arc stream. The current-density in the positive carbon is 
also increased to values of more than 800 amperes per square- 
inch. At this high current-density the crater of the positive car- 
bon burns out to a deep cup-like form within which the vapors 
of carbon and core material appear to be retained and possibly 
compressed by the stream of electrons from the negative carbon, and 
so raised to a temperature considerably above the vaporizing tem- 
perature of carbon. The effect of this action is to produce a brilli- 
ancy within the crater cup several times that possible at the positive 
crater of the low-intensity carbon arc. In these original high-intensity 
lamps the negative carbon was inclined to the positive and the 



July, 1940] PROGRESS IN PROJECTION LIGHTING 21 

latter rotated to maintain a symmetrical crater form. This method 
of operation is still used on lamps of higher power. Fig. 3 shows the 
appearance of this type of high-intensity arc as viewed from the 
side. 

The application of the high-intensity arc to projection through the 
medium of a condenser lens optical system gave three to four times 
as much light on the screen as had previously been available and 




FIG. 3. Photograph of d-c high-intensity arc in 
condenser- type lamp. 

further improved the efficiency of light production. Later improve- 
ments in the condenser lens system for high-intensity lamps have 
raised the efficiency of light production to more than five times that 
obtained from the earliest projection lamps. Thus improved, these 
lamps deliver possibly forty times the amount of light projected on 
the screens of the first motion picture theaters. 

One of the principal benefits realized from this enormous increase in 
screen light is the improvement in general illumination of the theater 
which followed. With only 200 lumens on the screen it was necessary 
for theaters, even of nickelodeon dimensions, to be operated in almost 



22 W. C. KALB [J. S. M. P. E. 

complete darkness. Many will recall the days when red exit lights 
were the only supplement to the dim illumination resulting from 
screen reflection. However, forty-fold increase in screen illumination, 
even on much larger screens, permits a clear picture to be shown in 
the presence of a comfortable level of general illumination, and the 
large theaters which adopted high-intensity projection were prompt 
in capitalizing this advantage. 

Small theaters could not afford these large high-intensity lamps, 
nor did they have need for so great a volume of screen light. The 
development of the reflector-type low-intensity lamp, however, 
brought to the small theater a considerable measure of improvement 
in screen light and permitted the installation of some general illumi- 
nation. In place of the condenser lens which, in the old type low- 
intensity lamp, picked up a light cone of approximately 45 degrees, the 
reflector lamp uses an elliptical mirror to pick up the light from the 
positive crater and focus it on the aperture plate. Both carbons are 
mounted in a horizontal position with the crater of the positive car- 
bon facing the mirror. By the adoption of this optical principle the 
light pick-up was increased from 45 to 120 degrees, and projection 
efficiency greatly improved. The needs of theaters requiring more 
light than this, but not large enough to require the condenser-type 
high-intensity lamps, were met in a similar manner by using the 
mirror principle with the high-intensity arc, in what is commonly 
termed the "Hi-Low" lamp. In this lamp the negative carbon is 
inclined to the rotating positive, but at a much smaller angle than in 
the condenser-type high-intensity lamp. The positive carbon used is 
9 mm in diameter, and the arc is operated at a current of about 75 
amperes; whereas the condenser-type lamp uses a 13.6-mm positive 
and an arc current of about 125 amperes. 

In the early 30's the increasing attention being given by the public 
to the subject of adequate illumination was becoming a serious prob- 
lem to a large number of motion picture theaters. Theaters using 
high-intensity projection had demonstrated the feasibility of main- 
taining a level of general illumination permitting comfortable vision 
on the part of patrons entering from the street or the brilliantly 
lighted lobby. Theatergoers were no longer willing to grope and 
stumble to their seats without complaint or to accept screen pro- 
jection of inferior quality. A clear screen image in the presence of 
adequate general illumination requires a screen brightness of at least 
7 foot-lamberts and preferably more. Low-intensity projection lamps 



July, 1940] PROGRESS IN PROJECTION LIGHTING 23 

will not provide this amount of light on the screens of many neigh- 
borhood houses that are, however, not large enough to require high- 
intensity lamps capable of giving 7 foot-lamberts on screens consider- 
ably more than 20 feet in width. Nor could a three- or four-fold in- 
crease in the cost of lamp operation be justified by these theaters of 
relatively small seating capacity. It was at this psychological time 
that the "Suprex" carbon was developed by the laboratories of 
National Carbon Company, Inc., and projection lamps of simplified 
design were produced to take advantage of its possibilities. The 
optical principle in these lamps is the same as that of the low-inten- 




FIG. 4. Photograph of "Suprex" type arc. 

sity reflector arc lamp, but a still larger angle of light pick-up has 
been adopted and improvements have been made which consider- 
ably increase the projection efficiency. These lamps use small- 
diameter, copper-coated, high-intensity carbons operating without 
rotation in a horizontal position, as seen in Fig. 4. Admirably meeting 
the needs of theaters of intermediate size, they have even reached 
into the fields formerly occupied by the earlier types of high-intensity 
lamps. These simplified high-intensity lamps occupy the wide gap 
between the maximum light output of the low-intensity lamp and the 
very high light output of the original high-intensity types. Further- 
more, the cost of operation is so low on these simplified high-intensity 
lamps that the advantages to be gained from increased screen light 



24 W. C. KALB [J. S. M. P. E. 

and better general illumination more than offset the slight increase 
over the operating cost of low-intensity lamps. 

Another factor which gives further advantage to theaters using 
high-intensity projection is the growing popularity of color features 
and the critical attitude of theater patrons toward accuracy of color 
reproduction. The audience sees on the motion picture screen only 
those colors that are present in the projection light. If certain colors 
are absent from the light, the dye on the film can not put them on the 
screen. Excess of certain colors likewise distorts the natural hues of 
color features. High-intensity carbon arc projection assures an evenly 
balanced light with all colors present in essentially equal intensity. 




FIG. 5. Color distribution of light from high-intensity carbon 

arc. 

This is apparent from the chart of color distribution shown in Fig. 5. 
This is the quality of projection light for which theatrical color-film 
is processed. It is the only quality of light that gives natural color 
reproduction with standard 35-mm color-film. Low-intensity lamps 
give a light of yellowish tint which distorts color values and detracts 
from the realism and beauty of color features. The high-intensity 
arc, emitting essentially equal intensities of all the spectral colors, re- 
produces all hues and tints with remarkable accuracy. 

Even though some theaters of small seating capacity may not have 
felt the need for the greater volume of screen light that has been ex- 
perienced by houses of greater capacity, they are feeling the need for 
a better quality of projection light than low-intensity lamps provide. 
The snow-white light of the high-intensity arc means just as much in 



July, 1940] PROGRESS IN PROJECTION LIGHTING 25 

the way of satisfied patronage and increased attendance to these small 
theaters as it does to the large down-town houses, and the latest 
development in projection equipment, the new low-wattage high- 
intensity arcs, puts high-intensity projection right in the lap of this 
smallest member of the theater family. Both a-c and d-c lamps are 
now on the market in which the power consumed at the arc is of the 
order of one kilowatt, and the cost of operation correspondingly low. 
The operating cost with these new lamps is less than that of the low- 
intensity lamp although the light output is 50 to 80 per cent greater 
and the efficiency of screen light production the highest yet obtained. 
Cost of operation is therefore no longer a justification for any theater, 
however small, doing without the increasingly important advantages 
of high-intensity projection. 

The new a-c high-intensity lamps avoid the flicker sometimes ob- 
served when the a-c high-intensity arc is operated on 60-cycle alter- 
nating current by operating through a frequency changer which 
supplies 96-cycle alternating current to the arc. The cut-off fer- 
quency of the two-blade shutter at standard projection speed is 48 
cycles per second. With a 60-cycle light-source, this results in a 12- 
cycle beat or fluctuation in the screen light which, under certain con- 
ditions, may be disturbing to the observer. By using a frequency of 
96 cycles at the arc one full cycle of current occurs during each 90- 
degree shutter opening, and disturbing flicker is eliminated. Re- 
gardless of the phase relation between the current and the shutter, 
the same amount of light is passed during each period the shutter is 
open. 

The new d-c high-intensity lamps are operated at 30, 35, and 40 
amperes arc current with 27.5 volts or less across the arc. This low 
arc voltage has been made possible by the development of an im- 
proved negative carbon which permits operation at short arc length 
without the formation of a carbide tip. The optical principle in 
these new low-wattage high-intensity lamps is the same as that 
used in the simplified high-intensity lamps which have achieved 
such popularity during the past four or five years. 

Reviewing on a more specific basis the foregoing narrative of prog- 
ress, five lines of improvement will be noted. These are (1) intrinsic 
brilliancy, (2} light quality, (3} volume of screen light, (4) efficiency 
of light production, and (5) economy of operation. 

(1) Intrinsic Brilliancy. In the early days of motion picture pro- 
jection, methods of light measurement now available had not come 



26 W. C. KALB tf. S. M. P. E. 

into use, but it seems probable that in the original low-intensity 
lamp the brilliancy of the positive crater was much lower than the 
values now attained. Later improvements in vertical trim lamps 
may have brought this value up to 150 cp/mm 2 and, in the low- 
intensity d-c reflecting arc a crater brilliancy of 175 cp/mm 2 is at- 
tained. This, as has been stated, is about the limit of brilliancy for 
the low-intensity d-c arc under stable operating conditions. The 
application of the high-intensity d-c arc to projection, about 1919 
or 1920, removed this fixed limit to crater brilliancy which is an in- 
herent characteristic of the low-intensity arc. High-intensity arcs 
are operated at crater brilliancies in excess of 800 cp/mm 2 and a re- 
cently developed super-high-intensity carbon for process projection 
can be operated at a brilliancy of 1200 cp/mm 2 , an 8:1 improvement 
over the early types of projection arcs. 

(2) Light Quality. Improvements in quality of projection light 
have been along two lines, improved steadiness and improved color. 
The earliest projection lamps used solid carbons for. both positive 
and negative electrodes. Due to a tendency for the arc stream to 
shift its position over the tip of the positive carbon, considerable 
unsteadiness in light output was experienced. This was reduced by 
the use of cored positive carbons. The effect of the core is to stabilize 
the arc stream at the center of the positive carbon face and thus im- 
prove the steadiness of burning. Further improvement in steadiness 
was effected by introducing a core in the negative carbon and later 
by substituting, for the plain negative carbon, equal to or near the 
diameter of the positive, a metal-coated negative carbon consider- 
ably smaller in diameter than the positive. This metal-coated nega- 
tive carbon, called the "Silvertip" carbon, was introduced about 
1916 or 1917. An improved metal-coated negative, the "Orotip" 
carbon, was developed several years later. 

Steadiness of the a-c low-intensity arc was improved in 1917 by 
the introduction of certain rare-earth materials in the core of the 
carbons. This material, by its arc-supporting properties, greatly 
improves the steadiness of burning on alternating current. It has the 
further advantage of giving a snow-white projection light. 
The neutral cored low-intensity arc, either a-c or d-c, gives a light 
of yellowish tint. The higher the crater temperature, the whiter the 
light produced, but at the maximum temperature attainable in the 
low-intensity arc the color composition on the basis of energy dis- 
tribution is approximately 18 per cent violet and blue, 32 per cent 



July, 1940] 



PROGRESS IN PROJECTION LIGHTING 



27 



green and yellow, and 50 per cent orange and red. The adaptation 
of the high-intensity arc to projection about 1919 or 1920 made a 
marked improvement in the quality of light. The striking difference 
in color composition between the low-intensity and the high-intensity 
arc is shown in Fig. 6.. It will be noted that the light from the high- 
intensity arc contains approximately equal proportions of all the 
primary colors. This quality of light proved much more pleasing for 
monochromatic pictures than the yellowish light from the low-in- 
tensity arc. With the introduction of color photography and the need 



34% 




35% 






31% 


VIOLET 




GREEN 




ORANGE 


AMD 




AND 




AND 


BLUE 




YELLOW 




RED 



18% 

VIOLET 

AND 

BLUE 



32% 

GREEN 

AND 

YELLOW 



50% 

ORANGE 

AMD 

RED 



HIGH INTENSITY LIGHT 



Low INTENSITY LIGHT 



FIG. 6. Comparison of color composition of light from 
high-intensity and low-intensity carbon arcs. 



for accurate color reproduction on the screen, the importance of 
snow-white projection light was increased, since all 35-mm film is 
processed for projection with light having approximately equal pro- 
portions of all the spectral colors. 

Sixteen-mm color-film, on the other hand, is usually processed for 
projection with incandescent light, the type of light at present most 
frequently used in 16-mm projectors. This light is even yellower 
than that of the low-intensity arc. Since 16-mm projectors are often 
equipped with carbon arc lamps to permit their use before gatherings 
of considerable size, a new carbon trim, known as the "Pearlex" 
trim, was developed in 1937 especially for 16-mm projection. The 



28 W. C. KALB [J. S. M. P. E. 

color composition of the light from this carbon, as now made, is pro- 
portioned to give accurate color reproduction with film processed 
for incandescent projection. 

(3) Volume of Screen Light. Although accurate records are not 
available, it seems probable that less than 200 lumens were projected 
upon the screen in the earlier motion picture theaters. This figure, as 
well as those on screen light which follow, are without shutter or film . 
When a shutter having 90-degree blades is used with no film, the 
figures will be reduced to one-half the values given. Further reduc- 
tion, varying in amount, results from the density of the film being 
projected. 

Improvements in carbons and in optical equipment of the old-style, 
vertical-trim projection lamps raised the available screen light to 
about 1600 lumens. The adaptation of the high-intensity arc to pro- 
jection about 1919 further increased the available screen light to 
about 5700 lumens and was a major factor in making possible the 
marked increase in seating capacity of motion picture theaters which 
characterized that period in the history of the industry. Later im- 
provements in the condenser system of the high-intensity lamps give 
almost 8000 screen lumens from a 13.6-mm high-intensity positive 
operating at 125 amperes. 

A development of great importance to motion picture projection 
was the reflecting arc lamp, adapted to the d-c low-intensity arc 
about 1924 and to the high-intensity arc, as the "Hi-Low" lamp, 
about 1926 or 1927. The optical principle of the reflecting arc 
lamp, by greatly increasing the angle of light picked up from the 
arc and projected upon the screen, made it possible to obtain 2000 
screen lumens from the d-c low-intensity arc, and subsequent im- 
provements in carbons have increased this figure to 2400 screen lu- 
mens. At 32 amperes of arc current the d-c low-intensity reflecting 
arc gives 50 per cent more screen light than the condenser-type low- 
intensity arc operated at 50 amperes. The simplified high-intensity 
lamps, introduced in the early 30's, are also of the reflecting type. 
They have a light output of 4300 to 7200 screen lumens. The light 
output from the new low- wattage high-intensity lamps lies between 
the above range and the 2400 screen lumen output of the low- 
intensity reflecting lamp. 

(4) Efficiency of Light- Production. Very striking improvement in 
the efficiency of screen light production has resulted from improve- 
ments in carbons and optical systems. The early low-intensity 



July, 1940J 



PROGRESS IN PROJECTION LIGHTING 



29 



lamps, using condenser lenses, gave, without shutter or film, less than 
0.1 screen lumen per line watt, which was increased by various im- 
provements in carbons and lamps to about 0.3 screen lumen per line 
watt. The condenser-type high-intensity lamps when introduced 
gave 0.4 screen lumen per watt, and subsequent improvement of the 
condenser lens system has brought this value up to 0.54 screen lumen 
per watt. The mirror arc lamp raised the efficiency of the d-c low- 
intensity arc to 0.65 screen lumen per watt, and increased efficiency 
of conversion equipment has made it possible to obtain 0.95 screen 



<i.3 

2.0 
1.5 
10 

0.0 
/I 








kiqhlntmsity 
Lomp 






D.C.Sim pli 
High Inttntily 


c te* 

LC/fi 


J^-X^^ 














D.C.Lo* Intensity 
e/k<.t,f!f /?/?c i. 

D. C High MerJiiiy 


">/>- J 






~=5. 


ConJfaiir Tfft ltm/3 

r 


^ 




00 1910 mo f930 /9< 



FIG. 7. Progress in efficiency of screen light pro- 
duction. 



lumen per watt. In the "Hi-Low" lamp an efficiency of 0.67 screen 
lumen per watt is attained. The development of a-c high-intensity 
carbons and "Suprex" carbons for d-c operation in the early 30's, 
and the production of simplified high-intensity arc lamps for use with 
these small-diameter copper-coated carbons, increased the efficiency of 
light production to values from 1.7 to 1.95 screen lumens per watt. 
In 1939 a new negative carbon, known as "Orotip" C, was intro- 
duced, which permits the operation of the high-intensity arc at 



30 



W. C. KALB 



[J. S. M. P. E. 



lower voltage than was previously practicable. New d-c high-inten- 
sity lamps have been developed to use this negative and a "Suprex" 
positive with a power consumption at the arc of little more than 1 kw. 
A new a-c lamp of low arc wattage has also been developed in which 
the flicker sometimes found objectionable in the 60-cycle high- 
intensity arc is avoided by converting the power applied to the arc 
to 96 cycles per second. These new, low- wattage, high-intensity 
lamps give efficiencies as high as 2.35 screen lumens per line watt. 



to 



40 



20 



r)00 
FIG. 8. 



/9/0 1920 1930 

Progress in economy of operation. 



The ratio of improvement in screen light efficiency from the earliest 
low-intensity lamps to the latest high-intensity lamps is approxi- 
mately 30: 1. Fig. 7 presents a graphic picture of the progress made 
in efficiency of screen light production. 

(5) Economy of Operation. The economy of operation that has 
been realized from the improvement in carbons and lamps can best 
be illustrated by a comparison based on current carbon prices and a 
uniform rate for electric power. As a representative figure a power 
rate of 4cf per kwh is assumed, given in the following tabulation : 



July, 1940] PROGRESS IN PROJECTION LIGHTING 31 

Cost per Hour per 1000 
Type of Lamp and Trim Screen Lumens 

(per cent) 

Early d-c low-intensity, condenser-type 100 

Later d-c low-intensity, condenser- type 72 

Early d-c high-intensity, condenser-type 58 

Present d-c high-intensity, condenser-type 42 

"Hi-Low," reflecting 36 

Low-intensity, d-c, reflecting 24 to 32 

A-c high-intensity, 60-cycle 19 to 21 

D-c simplified high-intensity 18 to 19 

New, low-wattage, high-intensity 14 . 5 to 18 

Fig. 8 is a graphic presentation of the 7 to 1 gain in economy of 
operation represented by the data in the foregoing table. 

When it is considered that the record of progress in the production 
and utilization of carbon arc projection light shows an 8:1 improve- 
ment in brilliancy of the source, a 30:1 improvement in the efficiency 
of screen light production, and a 40:1 improvement in the volume 
of light on the screen, together with marked improvement in color 
quality and steadiness, it must be recognized that projection lighting 
practice has kept fully abreast of progress in all other stages of the 
industry. A matter for further consideration is the fact that this 
tremendous technical advance in screen illumination has been ac- 
companied by a 7:1 reduction in operating cost for an equal volume 
of light on the screen. There are few, if any, factors associated with 
the operation of motion picture theaters for which such a striking 
record of progress can be cited. 



GASES FROM CARBON ARCS AND THEIR EFFECTS* 
A. C. DOWNES** 

Summary. This paper is a review of work done in the laboratories of National 
Carbon Company, Inc., the College of Medicine of the University of Nebraska, the 
School of Public Health of Harvard University, and the Department of Health of 
the City of Detroit on the products of combustion from carbon arcs used in the motion 
picture industry. Analyses of the gases coming from various lamps show that, even 
in the stacks, the only gas occurring in toxic concentration is nitrogen dioxide. 

The biological effects of undiluted stack gas from simplified high-intensity arcs 
upon experimental animals were only those due to the nitrogen dioxide. 

The arc-ash fume when administered by intratracheal and subcutaneous routes 
in rabbits was found to be relatively inert. 

Determination of nitrogen dioxide concentrations in poorly ventilated projection 
rooms failed to show any concentration more than about one-fifth that generally con- 
sidered as allowable for exposure of several hours' duration, and therefore there is little 
or no hazard in these projection rooms. 

Studies of ventilation under controlled conditions show that even with very low 
rates of both lamp house and room ventilation there is no danger of gases or fumes 
reaching concentrations which are toxic and that if sufficient ventilation is provided 
to produce comfortable working conditions there can not be any appreciable concen- 
trations of nitrogen dioxide or arc-ash fumes in the booth. 

From time to time in recent years, the question has been raised 
concerning the products of combustion of the carbon arc and their 
effect upon motion picture projectionists who work around arcs. 
Although many research workers of our company, including the 
author of this paper, have worked for years with carbon arcs under 
all kinds of operating conditions and under varying conditions of 
ventilation, no adverse effects have ever been noted. Naturally, 
therefore, it was not considered that there was any problem here. 

Nevertheless, in view of these recent requests for information, it 
has seemed desirable for us to support some independent investiga- 
tions along these lines, and to make some analyses in our own labora- 
tories. The results of these investigations, as they have become 

* Presented at the 1940 Spring Meeting at Atlantic City, N. J. ; received 
March 26, 1940. 

** National Carbon Co., Cleveland, Ohio. 

32 



GASES FROM CARBON ARCS 33 

available, have been published in various scientific journals as will 
be noted throughout the text of this paper. The conclusions, in- 
evitable in view of the long history of successful carbon arc usage, 
are most encouraging, and provide scientific justification for the con- 
tinued good health of those of us who have worked in this field for 
so many years. 

The literature on the carbon arc has many references to the gases 
evolved by arcs, the most frequently mentioned being nitrogen oxides, 
ozone, and carbon monoxide. A very careful investigation in our 
own laboratories has shown the presence of carbon dioxide and 
exceedingly small amounts of carbon monoxide, far below toxic range 
even in the undiluted stack gases; nitrogen oxides, but no ozone. 
Only the nitrogen oxides were found in toxic quantities and then only 
in the undiluted stack gases. 1 

Further study, using delicate spectrographic absorption methods, 
failed to show the presence of ozone, 2 and the statements in the 
literature which contradict this finding may well be due to the simi- 
larity of the chemical reactions of ozone and nitrogen oxides and the 
fact that their chemical separation is extremely difficult. 

Tests on stack gases from a 65-ampere arc burning 8-mm copper- 
coated positive and 7-mm copper-coated negative non-rotating high- 
intensity carbons failed to show the presence of either hydrocyanic 
acid (HCN) or cyanogen (C2N 2 ), and tests with ammoniacal silver 
nitrate solution indicated the absence of hydrogen sulfide, acetylene, 
phosphine, arsine, stibine, chlorine, and the other halogens. 

Table I shows the analyses of the gases evolved from the carbon 
arcs commonly used in the motion picture industry. The table shows 
the amounts of these gases in the lamp stack, and not in the room where 
the lamp was operated. It is very important that this distinction be 
kept in mind in the analysis of any data bearing on this question of 
gases from carbon arcs. 

The gas given off in largest amount in motion picture arcs is carbon 
dioxide, entirely innocuous in far higher concentrations than found 
in the gases from any arc. Only one investigator has apparently 
been able to detect any carbon monoxide in arc gases and even then 
rarely and in quantities even in the stack gas far less than the concen- 
trations generally considered safe for exposures of several hours' 
duration. 3 

The only other gas produced in measurable quantities in carbon 
arc lamps is the so-called "nitrogen oxides." This is the only one 



34 A. C. DOWNES [J S. M. P. E. 



Arcs Commonly Used in the Motion Picture Industry 

Heat 
Liberated Carbon Nitrog 
at Arc, Air Flow Dioxide Carbon Peroxi( 
'Current, Voltage, Btu through Lamp, COz Monoxide, NOz 
Amperes Volts per Min. Cu Ft per Min. (Per Cent) CO Ppm* Ppm* 

30 55 108 5.1 0.48 .. 270 


CO 


O5 

% 
3 

CO 




i 

d 

5 

oo 
co' 

S 


<M 

i i 

-f 

S 

CO 

CO 

cB 


1 ( 

d 

o 

1 

S 


8 

d 



or volumes of air. 


o 

l_ 

"c3 
'I 

1 
o 

ft 

1 
1 

o 
{3 

J 


8 
















V) 


'C 


1 


i 


c c 

3 'JS 


1 


d o 
d d 




d 


d 1 
dS 


d d 
d S d 


1 


c 
x 


1 
















.2 





t 


i 


bo en 


be 
1 


c/5 bo 


1 


II 


^ ^ 


1 


| 


5 
















ft 





^ 


I 6 


S 5 


S 


e B 





S S 


see 


i 


*7- 


I 


31 


6 6 
O <* 


1 


S g 


S 
cxb 


6 S 
ri co 


S 6 6 

2 CO S 


*o 

en 


5 


1 


1 


r-l ^ 


^ 






CO 


>^> 


V 


^ 




3 ' V 


*y 




o 


V 


a 


V 


1 


1 




o 


*d 




T) 




o 


d 


o 


^ 




ft 














t/3 




















r 


. 




^ 










>> 


>> 


S 


| 




.a 


<U 








"55 


'w 


1 







% 


S 








1 


a 
o 


i 






5 


1 




X 


X 




1 


& 


x 
H 




B 


'rS 




ft 


ex 


*bO 


*bO 


* 


* 



CO 



July, 1940] GASES FROM CARBON ARCS 35 

found in amounts which could be considered toxic, and then only in 
the undiluted stack gases. There are several oxides of nitrogen, but 
the only one directly formed by the action of the carbon arc in air is 
nitric oxide (NO). This gas, upon contact with the moisture and 
oxygen of the air, is immediately converted to nitrogen dioxide or 
nitrogen peroxide (NO 2 , N 2 O 4 ), and it is the concentrations of this gas, 
as NO 2 , that are given in the table. 

For prolonged exposure without hazard to human beings, Hender- 
son and Haggard 3 give a maximum concentration of 39 parts per 
million of nitrogen dioxide (NO 2 ) and the stack gases from the arcs 
given in Table I all contain more than this amount. However, an 

TABLE II 
Chemical Composition of Ash from the Arc 

Flue Lamp House 

Condensate Condensate 

Substance (Per Cent) (Per Cent) 

Silicon dioxide 1.79 1.21 

Rare earth oxides 65.70 71.80 

Ferric oxide 2.26 1.46 

Calcium oxide . 53 . 20 

Potassium oxide 2.26 2.38 

Sulfur trioxide 2.35 2 . 98 

Phosphorus pentoxide 0.17 0.15 

Fluorine* 10.65* 11.31* 

Boric anhydride . 50 . 60 

* Combined with the rare earths as the very insoluble fluorides. 



arc would have to be burned a very long time, even in a small room 
with practically no ventilation, before the room air would reach any 
such concentration. Moreover, in making the determinations re- 
ported in Table I, no ventilation of the lamp houses was provided, 
other than that induced by the heat liberated at the arc, in order to 
provide the highest possible concentrations of the various gases in 
the stacks so that the chemical determinations would be as accurate 
as possible. 

Generally speaking, the amount of nitrogen oxides increases with 
the arc wattage, while at the same wattage a low-intensity arc will 
probably produce more than a flame or a high-intensity arc. With 
a given arc, less nitrogen oxide is produced with a properly regulated, 
steady arc than with an unsteady one. 



36 A. C. DOWNES [J. S. M. P. E. 

In addition to the true gases produced by the operation of arcs in 
air, the volatilization in the arc of the rare earth metal compounds of 
the core materials of flame and high-intensity arcs produces a white 
smoke or fume which is made up of very small particles not more 
than 0.2 micron in size. 4 An average chemical analysis of these 
particles is given in Table II. 5 

Studies of the biological effects on experimental animals of the 
arc gases and fumes together, of the arc gases alone after removal of 
the smoke by filtration, of pure nitrogen oxides produced from nitric 
acid, and of the condensed ash from the fume, have been made by 
MacQuiddy, Tollman, LaTowsky, Bayliss, and Schonberger at the 
College of Medicine of the University of Nebraska, s- 6 - 7 - 8 - 9 

In their first experiments groups of albino rats and guinea pigs were 
exposed to the undiluted, unfiltered, complete stack gases from a non- 
rotating, high-intensity arc burning 7-mm X 12-inch-copper-coated 
positive and 6-mm X 9-inch copper-coated negative carbon electrodes 
at 40-55 amperes and 28-36 volts direct current. One group of 
animals was exposed for one hour per day, six days per week for a 
maximum of ten months; another group for four hours per day, 
six days per week, for a maximum of eight months; and a third 
control group was kept in the same room but not exposed to the arc 
gases at all. It was found necessary to cool the arc stack gases but 
otherwise they were just as they came from the arc. 

The flow of air and gases through the lamp, stack, and animal 
exposure chamber attached was at the rate of only 3.8 to 9.4 cubic- 
feet per minute, the average of 17 weekly flow tests being 6.1 cubic- 
feet per minute. The average content of nitrogen oxides (NO 2 ) was 
160 parts per million, varying from 100 to 205 ppm. The carbon 
dioxide content of the gas was from 0.245 per cent to 0.277 per cent. 
No carbon monoxide and no sulfur dioxide were found, and the 
authors, like ourselves, were unable to confirm the statements in 
the literature that ozone was present. 5 

In considering the conclusions resulting from this work it must 
be remembered that the exposures were in the undiluted stack gases 
with concentrations of nitrogen oxides more than four times as 
high as Henderson and Haggard's 3 recommended concentration of 
39 parts per million for safe prolonged exposure. 

The following are the exact words of the conclusions of MacQuiddy 
et al. as a result of this work. 6 

"(1) The undiluted gross fumes arising from an electric carbon 



July, 1940] GASES FROM CARBON ARCS 37 

arc are toxic to mice, rats, guinea pigs, rabbits, and cats, when inhaled 
under the conditions of exposure described. The pathology indicates 
that the oxides of nitrogen produced these changes. 

"(2) Undiluted gross arc fumes when inhaled for 1 hour a day 
for as long as 10 months produced no pathological changes in the 
tissues or blood morphology (structural characteristics) of guinea 
pigs. Under the same conditions albino rats died in a period of 11 
to 32 weeks' exposure with acute, sub-acute, and chronic lung in- 
flammations. 

"(3) Undiluted gross arc fumes when inhaled for 4 hours a day 
caused the death of 90 per cent of the guinea pigs exposed in from 2 
to 7 months. At a variable time after exposure began animals 
showed a gradual marked weight loss. They showed an increase 
in the leucocyte (white blood cell) count attributed to a polymorpho- 
nuclear leucocytosis, * increased non-protein nitrogen of the blood, 
and a decreased CO 2 combining power of the blood plasma. Tissue 
changes consisted of inflammatory changes in the upper and lower 
respiratory tracts, and fatty change in the livers. 

"(4) All the albino rats exposed 4 hours a day to the undiluted 
gross arc fumes died in from 1 to 16 weeks with marked inflammatory 
changes in the lungs." 

MacQuiddy et al. have run two similar series of animal experiments, 
one using the gases from the same arc from which the white fume was 
removed by filtration, and the other similar concentrations of ni- 
trogen oxides produced by the action of nitric acid on copper. Their 
conclusions from this work are: 9 

"First, the result of the inhalation of the carbon arc fumes filtered 
is very similar to the unfiltered arc fumes with the exception that the 
lungs do not show the number of dust particles in them that the lungs 
in the unfiltered arc fumes show. 

"Second, the results of the inhalation of pure chemically made 
nitrogen oxides were very similar to the result obtained from the 
filtered arc fumes. There being understood that the pure nitrogen 
oxides were used in as nearly the same concentration as the nitrogen 
oxides present in the concentrated arc fumes." 



* Polymorphonuclear leucocytosis the polymorphonuclear is the predomi- 
nating form of the white blood corpuscles and the term means an increase in the 
white blood corpuscle count due to the increase in this one dominant form of 
white blood cell. 



38 A. C. DOWNES [J. S. M. P. E. 

MacQuiddy and his associates attempted to determine the effects 
of the inhalation of the arc ash alone without the concomitant 
nitrogen oxides and carbon dioxide by exposing guinea pigs to the 
high-intensity arc ash collected from the lamp and stack, and kept 
in suspension in the exposure chamber by a fan. 7 The resulting con- 
centration of ash particles in the 2.3-cubic-foot chamber was enor- 
mous, varying from 12.8 to 24.7 milligrams per cubic-foot (451.8 to 
871.9 mg. per cu.-m.), which correspond to something between 192 
million and 864 million particles per cubic-foot. The very wide 
variation between these values is due to the uncertainty as to the size 
of the ash particles due to the agglomeration which occurs when the 
arc fume condenses on surfaces. Drinker and Snell 4 found only 
55.4 million particles about 0.2 micron in size per cubic-foot* at the 
image card of a non-rotating high-intensity arc lamp even with the 
insufficient stack flow of 7 cubic-feet per minute. It is therefore 
evident that the inhalation experiments of MacQuiddy and his co- 
workers were far more severe than any probable projection booth 
exposure. After exposures of 3 hours per day, 6 days per week, for 
6 months, and observations of some of the animals for 9 months 
afterward, no discernible changes could be found in the animals. 
The authors then raised the point that these experiments might not 
be directly applicable because of the fact that the ash particles were 
agglomerates and not of the size (0.2 micron) found in the arc fumes. 
They point out, however, that particles as small as 0.2 micron are 
not likely to be retained by the lung, and van Wijk and Patterson 10 
found that only 27.8 per cent of the 0.2-micron particles are removed 
by breathing dust-laden air. 

MacQuiddy and his associates also studied the effects of high- 
intensity arc and other arc ashes, using intraperitoneal (within the 
abdominal cavity) injection into rats and intratracheal insufflation 
(blowing into the windpipe) and subcutaneous injection in rabbits 
in comparison with several dusts of known effects. The technic of 
the intraperitoneal and intratracheal injections of dusts has been 
developed by physicians in order to obtain in a relatively very short 
time indications of the probable effects when human beings are 
exposed to air bearing such dusts in suspension. Generally speaking, 
results from intraperitoneal and intratracheal injections of dusts are 

* The New York State Code for Rock Drilling permits a concentration of 100 
million particles per cubic-foot if the rock contains less than 10 per cent free silica. 
The arc ash has a silica content which is much less than this. 



July, 1940] GASES FROM CARBON ARCS 39 

obtained in a few weeks or months which would take times of the 
order of 20 years by breathing dust-laden air. In considering results 
of these injection experiments one must always bear in mind that 
they are necessarily conducted on small animals such as white rats, 
guinea pigs, and rabbits. It is reasonable to suppose that reactions 
in still larger animals, man, for example, will be less violent than in 
rabbits. 

The conclusions of MacQuiddy et al. from this work are : 7 

"(0 The reaction to intraperitoneally injected silica, hematite, 
carbon, and talc in white rats corresponds to the reported results in 
guinea pigs. 

"(2) Tissue reaction in the peritoneal cavity of the albino rat 
was found generally to be more violent than the reaction either in 
the lung or the subcutaneous tissues of the rabbit. 

"(3) Some of the high-intensity carbon arc ashes appear to cause 
mildly proliferative reactions when injected intraperitoneally in the 
albino rat. The reactions to these arc dusts when administered by 
intratracheal and subcutaneous routes in rabbits are relatively inert. 

"(4) The rare earth metal salts, some of the carbon arc ashes, 
calcium phosphate, cupric oxide, and calcium fluoride appear to be 
essentially inert." 

The amounts of nitrogen oxides, other gases, and ash fume from 
arc carbon cores and their possible effects in concentrations found in 
the stacks from projection lamps are of great fundamental interest, 
but, after all, the important facts to determine are the effects that 
may be produced in the projection rooms themselves, some of which 
are much too small and lacking in adequate ventilation. Calcula- 
tions show that there is little probability of dangerous concentrations 
of nitrogen oxides being reached in even small motion picture pro- 
jection booths, but calculations are seldom as satisfactory as actual 
determinations. 

Fortunately we have the results of a very complete survey made 
by the Department of Health of the City of Detroit, Mich., of 147 
theaters in that city, which are reported in a paper read by William 
G. Frederick 11 before the American Conference on Occupational 
Disease and Industrial Hygiene in 1939 at Cleveland. It seems very 
probable that the conditions found in the Detroit theaters, which 
embraced all sizes, can be considered typical of the picture houses of 
the entire country, so that Frederick's paper is of significant value to 
the entire industry. 



40 A. C. DOWNES [J. S. M. P. E. 

The projection booths included in this investigation varied in size 
from 200 to almost 8000 cubic-feet and 105 of the 147 had volumes 
of over 1000 cubic-feet. Seventy-two had low-intensity lamps (de- 
fined by Frederick as less than 40 amperes), 37 had high-low lamps 
(defined as 40-85 amperes), 38 had high-intensity lamps- (defined as 
over 85 amperes), and 2 had arc type spot and special effect lamps 
only. 

TABLE III 
Showing N0 2 Concentrations Found 



Number 
Theaters 


Amper- 
age 


Stack Sample 
Actual 
Ppm 


Av. 
Ppm 


Booth Sample 
Actual 
Ppm 


Av. 
Ppm 


2 


15 


23, 23 


23 


1.6,0 


0.8 


3 


18 


202, 114 


158 


3.1, 3.1, 6.2, 6.2, 7.8, 4.7 


5.2 


14 


25 


None taken 




1.6, 2.2, 3.2, 2.2 


2.3 


16 


25 


24,46 


35 


3.2,0 


0.6 


21 


28 


238, 266 


252 


2.6, 1.6 


2.1 


25 


30 


113, 119 


116 


3.1,4.6,3.1 


3.6 


28 


32 


123, 123 


123 


0, 





29 


32 


134, 168 


151 


2.3, 3.1 


2.7 


30 


35 


88, 266 


177 


1.6, 3.1, 


1.6 


31 


40 


163, 7 


85 


1.6,0 


0.8 


32 


40 


24,46 


35 


3.1,0.7 


1.9 


33 


45 


79, 101 


90 


1.6,0 


0.8 


34 


45 


56,46 


51 


0,0 





35 


45 


38,22 


30 


2.4,0 


1.2 


36 


55 


24, 58 


41 


0,0,0 





37 


60 


25,23 


24 


0,0 





38 


65 


None taken 




0, 





39 


65 


39,39 


39 


3.1,3.13,3.1,6.2,3.1 


3.9 


40 


75 


363, 321 


342 


0,0 





41 


85 


26,22 


24 


0, 0, 3.0, 0, 0, 


0.5 


42 


120 


None taken 




0, 0, 0, 





43 


120 


9, 1 


5 


3.2,0 


1.6 


44 


120 


None taken 




3.2, 1.6, 0, 0, 0, 


0.8 


45 


130 


46 


46 


0,0,0 






Frederick describes and justly criticizes some of the ventilating 
systems used. However, we are primarily interested in his findings 
with regard to air contamination in the booth by gases from the 
arcs, with respect to which he has divided the booths into three 
classes, on the basis of fume odor. Class 1 (53 booths) nad satis- 
factory ventilating devices and no fume odor; class 2 (47 booths) 
had questionable ventilating devices and a slight fume odor; class 3 
(47 booths) had definite fume odor. 



July, 1940] GASES FROM CARBON ARCS 41 

Careful analyses of air from the worst booths, those of class 3 t 
showed that in no case was the nitrogen oxide concentration more 
than 8 parts per million, approximately one-fifth of the allowable 
concentration of 39 ppm for prolonged exposure. 3 Fifteen booths 
showed no measurable quantity of this gas, 32 less than 2 ppm, 41 
less than 5 ppm, and only 3 (6.4 per cent) had over 5 ppm. Table 
III gives the detailed results of these Detroit analyses. 

It was quite properly concluded that the low concentrations of 
nitrogen oxides found in even the poorly ventilated booths of class 3 
precluded any possibility of finding appreciable amounts of the gas 
in the better ventilated booths of classes 1 and 2. Frederick further 
states that no evidence of carbon monoxide poisoning was discovered 
among projectionists although no actual analyses for this gas were 
made. His conclusions are as follows: 

"The results of this fact finding study of the motion picture industry 
in Detroit indicate that no alarming health exposures are prevalent. 
The principal toxic agent to which workers are exposed is 'nitrous 
fumes.' Careful measurement of this exposure indicates it to be 
below the level usually considered harmful. Projection booths 
should be provided with adequate sanitary facilities, a suitable fresh- 
air inlet, and a positive pressure exhaust fan at the top of the fire 
stack. The present building code of the City of Detroit provides 
for these features. The study reveals the industrial hygiene of the 
motion picture industry in Detroit in general to be good." 11 

Unfortunately we have no data on concentrations of arc ash par- 
ticles in motion picture projection booths similar to Frederick's 
nitrogen oxide determinations. However, Drinker and Snell 4 of 
the Harvard School of Public Health have determined arc ash particle 
concentrations in a 3000 cubic-foot air-conditioned room in which 
the ventilation could be varied. A non-rotating high-intensity 
lamp with a ventilating flue was installed in this room, and connected 
so that the rate of air flow through the lamp house could be varied 
and controlled. This lamp was operated at about 62 amperes and 
43 volts with 8-mm X 12-inch copper-coated positive and 7-mm X 
9-inch copper-coated negative carbons. 

Operating with a controlled variety of ventilating conditions, 
Drinker and Snell 4 determined the numbers of ash particles at the 
image card on the lamp, at the operator's position, and in the room 
away from the lamp, before and after the lamp had been in operation 
for 30 minutes. Table IV gives their results with air flows of 7, 15, 



42 



A. C. DOWNES 

?!> s s s 



[J. S. M. P. E. 







July, 1940] GASES FROM CARBON ARCS 43 

and 50 cubic-feet per minute through the lamp house and 1000 cfm 
through the room. It is evident from the table that the particle 
count, even at only 7 cfm through the lamp, never approaches the 
New York State Code for Rock Drilling figure of 100 million particles 
per cubic-foot previously quoted, either near the lamp or elsewhere 
in the room. Table IV also shows the nitrogen oxide concentrations 
at the same locations and consideration of these together with the 
particle counts indicates that it would be impossible for the arc ash 
fume to reach any concentration even approaching a disagreeable 
condition. 

The amounts of less than 50 and less than 100 parts per million of 
carbon monoxide in the stack gases shown in Table IV are within the 
concentrations specified by Henderson and Haggard 3 for safe exposure 
for several hours. Moreover, Drinker and Snell explain these carbon 
monoxide values as follows: 

" carbon monoxide was followed by the Mine Safety Ap- 
pliances Company's indicator. MacQuiddy et a/. 6 point out that 
this latter device is inaccurate in the presence of nitrogen oxides and 
that actual concentrations are less than those shown by the indicator, 
the accuracy of which in our case was about 50 ppm for pure carbon 
monoxide." 

Their values are absolute maxima which even themselves are 
safe for several hours' carbon monoxide exposure direct in the stack 
gases. 

Drinker and Snell show that with a flow of 12 to 15 cubic-feet of 
air per minute through the lamp house there is no sensible escape 
of nitrogen oxides or other substances into the room; therefore if 
this minimum requirement is met there can be no question of any 
industrial hazard in a motion picture booth and, as a matter of fact, 
there probably is no hazard under much worse conditions than this, 
as shown by Frederick's survey in Detroit. 11 

In spite of the fact that there is probably no serious hazard in 
even a very poorly ventilated booth, the necessity and desirability 
of adequate ventilation should really rest on grounds entirely separate 
and apart from the gas and fume consideration. The proper ap- 
proach to the solution of projection booth ventilation should be from 
the general standpoint of providing reasonably comfortable working 
conditions for the projectionist. If this be done, and even if the 
draft through the lamp house should be inadequate completely to 
eliminate the arc gases from the room, they can not possibly approach 
an objectionable concentration in the booth. 4 Table V shows the 



44 A. C. DOWNES [J. S. M. P. E. 

effect of the draft through the lamp house on the concentration of 
nitrogen oxides in the booth, and the amount of booth ventilation 
which must be provided to give temperature rises of 5, 10, 15, 
and 20 F in the room with a simplified high-intensity arc. 

Table V shows very clearly the great effect of the rate of air flow 
through the lamp house on the air required for adequate booth 
ventilation. The amount of air required depends only on the heat 
liberated by the arc and if this is eliminated by ventilation there is 
no problem of gas removal. 

TABLE v* 

Summary of Roi,m and Flue Ventilation Requirements 

Temperature Flue 

Rise in Room, Ventilation, 

F Cfm 

5 

5 15 

5 50 

5 100 

10 

10 15 

10 50 

10 100 

15 

15 15 

15 50 

15 100 

20 

20 15 

20 50 

20 100 

In regard to the possibility of harm to the operator from presence 
of toxic fumes in the booth, it should be remembered that for many 
years the concentration of 39 parts per million of nitrogen dioxide 
has been considered safe for continuous exposure. 3 Table V shows 
that with no flue ventilation with 20 rise in room temperature and a 
room ventilation in the booth of only 545 cubic-feet per minute, 
less than one-tenth of the permissible limit of nitrogen dioxide would 
be present. If there is a ventilation of only 15 cubic-feet per minute 
in the lamp flue and a temperature rise of 5 in the booth, only 0.26 
part per million of nitrogen dioxide will be present in the room air, 
that is, 1 /i6o of the recognized safe limit for continued exposure. 

Table VI gives the ventilation necessary to hold the temperature 



Room Ventilation, 
Two Lamps 
(Alternating) at 
187 Btu/Min . 
Cfm 


Calculated 
NOz in Room, 
Ppm 


2130 


0.87 


1810 


0.26 


1300 





920 





1090 


1.76 


905 


0.51 


650 





460 





727 


2.64 


603 


0.77 


433 





307 





545 


3.53 


452 


1.01 


325 





230 






July, 1940] 



GASES FROM CARBON ARCS 



45 



SO o iO O 
2 ^ N * 






S S 8 8 fe S3 

i I CO Ci ^ CO 



CO CO 00 



o 



^ 10 '- t oo S 
co ^ o co -^ ro 



I 




.5 
5 

OS 

.1 

5 

3 

ex 



35 



43 



eg 



43 ^5 H 

bo bo * 

3 5 



46 A. C. DOWNES [J. S. M. P. E. 

rise to 5F in a projection room with 15, 50, and 100 cubic-feet per 
minute through the lamp house for the common types of arc used 
in projection. In calculating the air required the losses through 
the walls of the booth were considered negligible. These values are 
for a 5F rise only but the ventilation for any other temperature rise 
can be easily calculated. For example, a rise of 10F will require 
only one-half as much air through the booth as for 5F rise. 

Table VI shows very plainly that the amounts of air required to 
give safe, comfortable working conditions (a 5F temperature rise 
in the booth) are not excessive and the results that will be obtained 
should appeal to both projectionists and theater owners. 

Studies of ventilation under controlled conditions show that even 
with very low rates of both lamp house and room ventilation there 
is no danger of gases or fumes reaching concentrations which are 
toxic, and that if sufficient ventilation is provided to give comfortable 
working conditions there can be no appreciable concentrations of 
nitrogen dioxide or arc ash fumes in the booth. 

REFERENCES 

1 COLTMAN, R. W.: "Gases from Carbon Arcs," Jour. Ind. Hyg. and Tax., 
XX (April, 1938), p. 289. 

2 COLTMAN, R. W., AND MACPHERSON, H. G.: "Gases from Carbon Arcs: 
Absence of Ozone," Jour. Ind. Hyg. and Tox., XX (Sept., 1938), p. 465. 

8 HENDERSON, Y., AND HAGGARD, H. W.: "Noxious Gases," A. C. S. Mono- 
graph (1927). 

4 DRINKER, P., AND SNELL, J. R.: "Ventilation of Motion Picture Booths," 
Jour. Ind. Hyg. and Tox., XX (April, 1938), p. 321. 

6 MACQUIDDY, E. L., TOLLMAN, J. P., LATOWSKY, L. W., AND BAYLISS, M.: 
"Combustion Products of the Carbon Arc," Jour. Ind. Hyg. and Tox., XX (April, 
1938), p. 312. 

6 MACQUIDDY, E. L., TOLLMAN, J. P., LATOWSKY, L. W., AND BAYLISS, M.: 
"Biological Effects of Inhalation of Carbon Arc Fumes," Jour. Ind. Hyg. and Tox., 

XX (April, 1938), p. 297. 

7 MACQUIDDY, E. L., TOLLMAN, J. P., LATOWSKY, L. W., AND SCHONBERGER, 
S. : "Tissue Reaction of Some Carbon Arc Dusts," Jour. Ind. Hyg. and Tox., 

XXI (Dec., 1939), p. 498. 

8 TOLLMAN, J. P., MACQUIDDY, E. L., AND LATOWSKY, L. W. : "Acute 
Poisoning in Animals after Intraperitoneal and Intratracheal Administration 
of Dusts," Jour. Ind. Hyg. and Tox., XXI (Dec., 1939), p. 514. 

9 MACQUIDDY, E. L., TOLLMAN, J. P., LATOWSKY, L. W., AND SCHONBERGER, 
S.: "Biological Effects of Filtered Arc Gases and Pure Nitrogen Oxides," 
(from unpublished ms.). 

10 VAN WIJK, A. M., AND PATTERSON, H. S.: "The Percentage of Particles 
of Different Sizes Removed from Dust Laden Air by Breathing," Jour. Ind. Hyg. 
and Tox., XXH (Jan., 1940), p. 31. 

11 FREDERICK, W. G.: "A Study of the Motion Picture Industry in Detroit," 



July, 1940] GASES FROM CARBON ARCS 47 

read before the American Conference on Occupational Disease and Industrial 
Hygiene, Cleveland, Ohio (1939). 

DISCUSSION 

MR. FRANK: I suggest that it might be a good idea to consider reprinting in 
our JOURNAL the paper on the survey of the Detroit theaters. It would be of 
interest to all of us, although perhaps the most important facts have already been 
. given us by Mr. Downes. 

MR. DOWNES: A very considerable part of that paper is concerned with sani- 
tary conditions of booths which no doubt would be of interest here, but I have 
abstracted very carefully the part of the paper dealing with any possible hazards 
and have quoted verbatim the important data and conclusions. 

MR. KELLOGG: Nothing has been said about the fact that the psychological 
effects of fumes that one can smell may be much more serious than the actual 
physical effects. Human beings do have imagination, and imagination can cause 
serious physical effects. It is not quite fair to ask a man to work under conditions 
where you have to prove to him by tests on guinea pigs that those conditions are 
entirely healthful. The story of the tests on guinea pigs and white rats will go a 
certain way toward removing the fear of persons having their health affected be- 
cause they smell fumes. But we must not get the idea that that is all that is 
necessary. The results of the tests are very interesting and significant, but in my 
estimation it is still important to provide such good ventilation that no one work- 
ing in the booth will ever begin to worry about whether the fumes are harmful or 
not. 

MR. DOWNES: In replying to Mr. Kellogg's question I wish to emphasize 
the several statements in the paper that the guinea pigs and rats were exposed to 
undiluted stack gases with a very low rate of air flow through the lamps to ob- 
tain high enough concentrations of nitrous oxides to have definitely positive 
effects on the animals, and that these concentrations were many times those 
found in the survey of projection booths in Detroit. 

We have pointed out in the paper that ventilation should be provided in pro- 
jection rooms, and that the amount of ventilation should be determined by the 
volume of air necessary to provide bodily comfort to the projectionists, and not 
upon the presence or absence of fumes. If this basis be used, there can be ab- 
solutely no concentrations of fumes in such projection rooms which would be 
noticeable even to the most delicate sense of smell. Under such conditions the 
psychological effects, if any, of smelling disagreeable odors would be entirely 
eliminated so far as fumes from the lamps are concerned. 

MR. RICHARDSON: I have always advocated good conditions in projection 
rooms, but sometimes I have wondered whether we have not been little over- 
nervous of the gas fumes. In the old days we worked in rooms that had no special 
ventilation. The fumes from the arc all went all over the room. I worked under 
such conditions for four years, and yet am pretty healthy. 

If our present projection rooms are well ventilated, as they should be, and the 
lamp house is piped to the open air outside the theater, I can not see any danger to 
anyone who has anything like normal health. 

MR. DOWNES: I was very much impressed by the fact that the pictures of 
early projection rooms shown earlier by Mr. Richardson showed a complete 
absence of ventilation of lamp houses but Mr. William Reed who began operating 
in 1896 is here this afternoon and is still operating. 



AUDIENCE NOISE AS A LIMITATION TO THE PERMISSIBLE 

VOLUME RANGE OF DIALOG IN SOUND MOTION 

PICTURES* 



W. A. MUELLER** 

Summary. A series of noise measurements were made in theaters to determine 
the cause of low intelligibility of dialog recordings of wide volume range. Audience 
noise level was found to be a serious restriction, because it averages 8 db louder than 
film noise level and reduces the useful volume range by that amount. Audience noise 
is an extremely variable factor, as measurements made in the same theater showed it to 
be as low as the film noise in one instance and later to rise 14 db above this value. To 
secure good intelligibility, the volume range of the dialog must be compressed so that 
the softest-spoken words never are so low in level as to be seriously masked by audience 
noise. 

Sound engineers have been striving since the introduction of sound 
in motion pictures to extend the volume range of recording systems 
for the purpose of enhancing the dramatic and comedy possibilities 
of the sound and affording the actor and producer a better medium 
for presenting their story. 

Constant research and development by sound equipment manu- 
facturers and motion picture studio engineers have resulted in the 
invention of noise reduction, quieter film stocks, better developing 
and printing machines, improved photoelectric cells, vacuum tubes, 
and other items too numerous to mention, each of which has con- 
tributed to a reduction of the reproduced noise level of the recording, 
and therefore to an increase in volume range. 

This fine work has resulted in an overall linear recording system 
with a greatly extended volume range, and scenes heretofore lifeless 
and flat can now be presented with greater emotion and realism, and 
as a consequence have greater dramatic value. The increased dra- 
matic value of the wide-volume-range recordings was quickly realized 
by the actor and the director, and soon many scenes were being 
staged to take advantage of it. 

* Presented at the 1940 Spring Meeting at Atlantic City, N. J. ; received 
March 22, 1940. 

** Warner Bros. Pictures, Inc., Burbank, Calif. 

48 



AUDIENCE NOISE 49 

When pictures recorded with this extended volume range were 
first released, sound engineers and theater managers complained that 
these recordings were hard to understand. This factor of low in- 
telligibility was not noticeable in studio review rooms and was not 
particularly bad in empty theaters ; but in a theater with an audience 
present there was considerable dialog that was hard to understand. 
This was not only true from scene to scene, but was even more dis- 
turbing in the loss of intelligibility from word to word. 

Some words uttered by the characters on the screen could be 
clearly understood, while others seemed to be absorbed and entirely 
removed before they reached the audience. In effect, the audience 
was acting as a selective filter which suppressed certain words and 
permitted others to pass through to the listener. This was especially 
pronounced at the end of the sentences where many actors have a 
tendency to lower their voices and trail off into almost inaudible 
sound. 

In some theaters it was found that the intelligibility could be im- 
proved by raising the normal fader settings ; but when this was done 
the louder sequences in the picture, particularly the opening title 
music, overloaded the amplifier equipment. In other words, the 
amplifier capacity of these theater equipments was not adequate to 
reproduce pictures with a wide volume range. In other theaters 
where adequate power was available there was considerable audience 
annoyance because the high-level portion of the dialog became ex- 
plosive and disagreeable and the actors sounded as if they were 
"barking" at one another. 1 The immediate remedy was to raise 
and lower the sound level manually, effectively reducing the volume 
range. While this necessary compression of the volume range was in 
direct contradiction to the premises on which the new recording 
system had been developed, there was no denying that the manually 
compressed dialog recordings had higher intelligibility and were 
less "explosive" in the theater than those of wider volume range. 

Since this loss of intelligibility was not apparent in studio reviewing 
rooms, and was not definitely pronounced in empty theaters, it must 
have been due to the theater audience and was undoubtedly caused 
by the masking effect of audience noise. That is, the audience noise was 
sufficiently greater in intensity than certain syllables or words of the 
dialog so as to make them unintelligible, or even to eliminate them 
entirely. In other cases, entire scenes and sequences which were 
spoken very softly were so badly masked by audience noise as to 



50 W. A. MUELLER |j. s. M. P. E. 

cause complete lack of intelligibility and, consequently, the loss of the 
story sense of the production. 

That the above explanation was true was not apparent even to the 
most experienced listener, and it was decided to make a series of noise 
tests to confirm this theory. Table I shows a series of noise mea- 
surements taken in several theaters and studio review rooms, for this 
purpose. These measurements were made with a General Radio 
Type 759 Sound Level Meter, using the weighting networks as indi- 
cated. This instrument is calibrated on the basis of a zero reference 
level of 10~ 16 watt per sq-cm. The figure shown for each theater 
represents the average of a large number of readings taken at different 
positions in the auditorium. Measurements of the audience noise 
level were taken when silent trailers were being run or in a silent 
period between different portions of the show. A silent period of 30 
seconds was secured by delaying the start of the next feature, keeping 
the house lights and the screen dark. 

It should be noted that the noise level of the empty theaters is 
quite uniform, averaging +25 db. Also, the noise level is increased 
to +30 db when the ventilators are turned on. The noise caused by 
the audience, however, is surprisingly high, averaging +42 db and 
masking all other types of noise. Audience noise also is subject to a 
wide variation, rising to as high as +48 db at the end of the main 
feature when many people were leaving and entering." A measure- 
ment of +32 db was also obtained during a very dramatic sequence 
when the audience was unusually quiet. The figure of +42 db was 
the average of many such readings. 

The average level for dialog was +65 db, and loud music reached a 
level of +74 db. The loud music consisted of opening and closing 
title music and musical numbers, which are the loudest portions of any 
sound film and are recorded at 100 per cent modulation. 

These measurements show that a range of only 32 db is available 
between the loudest music reproduced in these theaters and the level 
of the audience noise. It has been found that the dialog should be at 
least 6 db above any noise level in order to be clearly understood. 
This requirement would mean that the absolute minimum level of the 
dialog should be +48 db. Since the maximum level in the auditorium 
which is attained at 100 per cent modulation of the film was +74 db, 
the usable volume range remaining is only 26 db. 

This means that dialog which can be clearly understood in a theater 
must never fall more than 26 db below 100 per cent modulation of 



July, 1940] AUDIENCE NOISE 51 

the recording medium, as any words or scenes which fall below this 
level will be masked by audience noise and not understood. The 
only way that this permissible volume range for dialog can be in- 
creased is to reduce the noise level in the theater or to increase the 
maximum loudness that can be tolerated on dialog. The audience 
noise level is very difficult to control and since psychological and 
physiological factors determine the annoyance caused by loud sounds, 
it appears that there is no easy way to extend this volume range. 

Inspection of Table I shows also why the intelligibility of the high- 
volume-range recordings was not impaired in the studio review rooms 
where, without an audience, the noise level is at least 15 db below 

TABLE I 

Theater Sound Level Measurements 

Venti- Audience Dialog Loud 

Theater Quiet lators on Noise Level Music 

. 40 Db Weighting Network ^70 Db Weight Network * 

Huntington Park +28.8 db +30.5db +43 db +64 db +74 db 

Granada +23.7 +26.8 +41 +69 +73 

Downtown +25.2 +34.5 +43 +66 +74 

California +25.6 +29.2 +38 +60 +72 

Mission +24.3 +32.4 +44 +65 +72 

San Pedro +25.0 +28.3 +40 +62 +72 

Hollywood +24.0 +28.1 +44 +62 +76 

Averages +25.1db +30.0 db +42 db +65 db +74 db 

Studio Review Room No. 4 +26 db ... +66 db +76 db 

Studio Review Room No. 5 +24 . . . +65 +75 

Zero Power Level = 10~ 16 watt per sq-cm. 

that of the average theater. This results in a usable volume range 
of 40 db, permitting the low-level syllables, words, or scenes, which 
are lost in a theater, to be clearly understood. 

Several pictures were recorded and released with dialog of reduced 
volume range, based on the above analysis (see Table I), and excellent 
results were immediately obtained. Complaints on lack of intelli- 
gibility ceased, and the reports showed that cueing of the sound 
level of these pictures, in the theaters, was no longer necessary or 
being practiced. As a result the procedure was adopted universally 
for all Warner Bros.' releases, and at present the volume range of the 
dialog in our pictures is limited to 25 db. This restriction of volume 
range is secured by means of electronic compressers which are in- 
stalled in all recording channels. 



52 



W. A. MUELLER 



IJ. S. M. P. E. 



While it has been found impossible to use the full volume range of 
the recording system for dialog because of audience noise, the present 
dialog recordings are still of greater range than those formerly re- 
leased, and many fine comments on their naturalness and dramatic 
qualities have been received. 

It should be emphasized that only the volume range of dialog has 
been under consideration, and our conclusion is that there should not 
be more than 25 db difference between the softest whisper and the 



-+60 



-I-JO 



7~,-n.c 
'K*>t, 
C/OO 96 Sv7 



FIG. 1. Volume characteristics of Warner Bros.' 
recordings. 



loudest spoken word. The relation between the loudness of average 
dialog and opening or closing title music or musical numbers, has not 
been discussed but our measurements show that for Warner Bros.' 
pictures, it averages about 9 db (see Fig. 1). The producers and 
studio executives would like this figure increased, but so many com- 
plaints are received that the music is too loud whenever this is done, 
that a compromise has been made on the above figure. Many of these 
complaints come from exhibitors with old or obsolete sound equip- 
ment, which overloads on the high-level passages. Until these equip- 



July, 1940] AUDIENCE NOISE 53 

ments are replaced, the dramatic effect desired by the producers 
can not be put into motion pictures. 

There is also another serious limitation to the most dramatic use 
of sound in motion pictures, and that is because even our present 
recording systems do not have sufficient volume range to accommo- 
date loud explosions, battle scenes, earthquakes, and so on. Many 
theaters with modern equipment cue these scenes by raising the level 
as much as 10 or 12 db, resulting in a much more dramatic and effec- 
tive presentation. In order to accommodate these sounds the level 
difference between normal dialog and 100 per cent modulation should 
be increased from 9 db to 20 db. The acoustic level of the loudest 
sounds could then rise to +84 db instead of + 74 db as at present. 
The sounds which would rise to this level would be sound effects 
only, as experience shows that audiences object strenuously to music 
which rises even 2 or 3 db above the loudness of present title music, 
i. e., +74 db, as measured in the auditorium of the theater. The 
lowest dialog should not fall below +48 db or 6 db above audience 
noise, and it should be compressed into a 25-db range. The film 
noise should be 8 db below the audience noise, or at a +34-db level, 
so that it does not contribute materially to the noise level of the 
theater. 

The volume range of such a recording system would be 50 db, and 
this should be secured from prints after a number of runnings in 
theaters, and not as they come from the release laboratory. This 
would be a 10-db improvement over the volume range of our present 
recording system, which averages 40 db, based on the noise level of 
prints after numerous runnings in theaters. Such a new recording 
system would meet every demand of the producers and exhibitors, 
but recordings made in this manner could not be reproduced on the 
obsolete, under-powered equipment now in many theaters. Studio 
sound engineers and equipment manufacturers are diligently working 
to perfect such a system, which when developed will further enhance 
the dramatic possibilities that sound has given to the motion picture. 

REFERENCES 

1 AALBERG, J. O., AND STEWART, J. G. : "Applications of Non-Linear Volume 
Characteristics to Dialog Recording," J. Soc. Mot. Pict. Eng., XXXI (Sept., 
1938), p. 248. 

2 LEVINSON, N. : "A New Method of Increasing the Volume Range of Talking 
Motion Pictures," /, Soc, Mot. Pict. Eng., XXVI (Feb., 1936), p. Ill, 



54 W. A. MUELLER [J. S. M. P. E. 

DISCUSSION 

MR. ALBERSCHEIM: Have other studios, using other recording methods, had 
the same experiences with the audience, and is the wearing of film, as well as the 
masking of the audience noise, selective to the recording methods used? 

MR. MUELLER:* We experienced this difficulty only when we began using a 
recording system having available a wide volume range. We were impressed 
with the dramatic results of these wide-range recordings and began releasing 
pictures in the theaters with the results outlined in my paper. 

In order to determine why this effect had not shown up in our previous record- 
ings with the variable-density system, we measured the volume range of a number 
of our pictures previously released and found that they were compressed into a 
narrow volume range much more restricted than I recommend in my paper. This 
was found to be true also of the recordings of all producers using variable-density 
sound and can be very easily verified by anyone with a true instantaneous peak- 
reading volume indicator such as the neon volume indicator which we use. 

Going still further, we determined that the cause of the compression in our 
own variable-density recordings was (1) compression due to the photographic 
characteristic, and (2} volume limiter action due to overloading by as much as 
8 or 10 db. At that time (1936) we reduced the percentage modulation in our 
variable-density recordings, as read by a neon volume indicator, so that no over- 
loading took place, and we found that much of the compression disappeared, 
but that due to the 8-db drop in recording level, the reproduced noise was too 
high to be satisfactory. 

As previously pointed out, 2 a variable-density recording with the same per- 
centage modulation should be about 8 db lower in level than a variable-area 
recording. The variable-density recordings being released in Hollywood at 
present run on the same fader settings as our variable-area recordings, indicating 
that the limiter type compression mentioned above is still present, and peak- 
reading volume indicator measurements also show that the variable-density 
pictures still have the greatly restricted volume range. Consequently, producers 
using variable-density records have not had this difficulty because their record- 
ings are compressed more than the ranges recommended in my paper, with the 
consequent penalty of serious overloading not present in properly produced 
variable-area recordings. 

MR. KELLOGG: I gather that there is not much that can be done toward 
reducing audience noise. Presumably that is true from the standpoint from which 
the paper is written, namely, what can the producers do about it? However, 
there is no question that greater sound absorption in the theaters would very 
materially reduce audience noise. The audience is competing with itself to be 
heard. People talk to each other, and the louder the noises from other sources, 
the louder they talk. There is further quieting of the audience due to the psy- 
chological effect of removing sources of noise such as ventilation systems, and of 
reducing noise by means of absorption. I should think that the possibility of 
increasing the volume range by means of sound absorption and making it up 
by more output in the sound system certainly looks hopeful. 

* Communicated, 



July, 1940 J AUDIENCE NOISE .V) 

DR. GAGE: In the reviewing rooms would it be desirable to have a sound- 
source equivalent to an audience, so that the reviewers might judge whether the 
dialog in the films was of correct volume to be intelligible in spite of this inter- 
ference? 

MR. RYDER: It is very difficult to judge playing levels in a review room where 
one is deprived of audience reaction. I have been following previews ever since 
the advent of sound, and even now I find that I miss in level settings prior to the 
first preview. I still depend upon hearing the picture with an audience for the 
establishment of the proper playing level. 

MR. MUELLER:* The measurements were averages of tests made in a number 
of theaters with different types of audiences and different types of pictures. 
Audience noise varies with the type of audience, the type of picture, and the 
scenes in the picture, and as stated in the paper, noise levels were found as low 
as +32 db and as high as +48 db. We can not make our pictures to suit the 
best or the worst noise conditions prevailing in the theaters, and we selected an 
average noise level as being the most logical compromise. 

I do not agree with a suggestion that has been made that the signal level be 
dropped 12 or 15 db below the audience noise. An audience may quiet down 5 
or 6 db for a dramatic, low-spoken scene if the scene is not too long. However, 
as soon as the scene is over, the noise level will rise above normal as the people 
readjust themselves in their seats and make themselves comfortable again. 

Any producer who released pictures based on the premise that the audience 
must be very quiet to enjoy them would be facing disaster. It has been our ex- 
perience that the product must be fitted to the requirements of the average 
theater and theatergoer rather than that the audience must be conditioned or 
educated to suit the picture. We know of no formula to make an audience be- 
have in a manner to suit the ideas of a producer of pictures. 

MR. ALBERSCHEIM: The wear of a film depends upon the type of track and 
other factors. Also, as has been pointed out, audience noise is selective to the 
dramatic content of the story, and perhaps in some theaters, if the story is a good 
one, the audience noise may be found at a level of only 32 db. Have other studios 
had the same experience with regard to volume range, or have you been able to 
put more volume range on your film without difficulty? 

MR. RYDER: Actually we have experienced a slight decline in volume range or 
in volume output from film, but not as a result of wear. The decline is the result 
of oil stains, and stains resulting from cleaning. Many of the cleaning processes 
are merely smearing processes. 

I hesitate to express a definite opinion regarding the desirable volume range of 
the future. The desirable volume range will depend upon the theater's carrying 
capacity. Mr. Mueller pointed out that Warners are at the moment limiting 
their volume range to meet the conditions in the field. Our activity at Para- 
mount has been one of pushing the theaters a little, with the hope of bringing 
more theaters into line so that they can reproduce sound to better advantage and 
put on a better show. 

MR. FRIEDL : It seems significant that the average dialog level was tabulated 
at +65, which is the reference reading on the noise-meter or the measuring in- 
strument, as acoustic energy in the auditorium. I believe the author also said 
they could not raise the average level of dialog. Let us assume that modern 



56 W. A. MUELLER [J. S. M. P. E. 

theater equipment provides adequate capacity and power for that average 
dialog range. We are still limited in the volume range of dialog by the noise 
coming up to meet it. The increase in power will, perhaps, lend more dramatic 
effect to the music. But what about the dialog? We can not have average dialog 
at a shouting level; it has to be convincing. 

MR. RYDER: In the Spawn of the North we had important dialog occurring 
during the crashing of icebergs and other loud-effects parts of the picture. In 
certain theaters one would hardly know there was any dialog because the effects 
so overloaded the equipment. In other theaters the dialog was distinctly heard 
and understood by the audience, carrying real meaning and adding dramatic 
value to the story. There is reason for having power beyond what is required 
for normal dialog reproduction. In general, I agree that dialog should not be 
pushed to levels where it is no longer real or convincing to the audience, although 
at times we have probably offended, along with others, in that regard. 

MR. OFFENHAUSER: Where do you place a measuring microphone in a case 
like this; and what sort of microphone do you use? 

MR. MUELLER:* The microphone was placed in the center right and left 
sections of the seats in the main floor of the theater or in the balcony. A series 
of measurements was taken with the microphone one-fourth of the way back 
from the front seats and also at a position three-fourths of the way back. The 
measurements given are averages of six positions in the case of a stadium type 
theater or twelve positions if the theater had a balcony. A crystal microphone is 
used. 

MR. FRIEDL : In the data presented the dialog and music, as measured in the 
same units, were run at about the same level, that is, in both the theater and re- 
view room. I think I recall seeing +74 as the level. Can you operate at as 
high an output level in the small room as in the theater? 

MR. RYDER: The output level from the horn no; the actual level to the lis- 
tener yes; even higher in small review rooms, before it becomes objectionable. 

MR. FRIEDL: You are not overriding audience noise there, because the noise 
of the room is less. There were no measurements of an audience in the small re- 
view room. There must be an audience, of course, but it is negligible in terms of 
numbers, for noise. 

Mr. Mueller points out that in trying to take advantage of all the new fine- 
grained emulsions, and the low noise of the amplifier systems, as these factors 
contribute to extending the volume range, we find that the limiting factor seems 
to be the audience noise; we have to do something to quiet the audience 
perhaps by putting carpet underneath the seats, or something like that. Evi- 
dently merely increasing the power output will not accomplish the desired result. 

MR. RYDER: We have encountered still a different factor in suppressing noise 
by acoustic treatment. The Arlington Theater in Santa Barbara was recently 
treated, at a cost of about $16,000, and has since not been desirable for previews. 
The deadening of the house has created an unfavorable situation. Although it is 
not completely dead, it is so dead that the audience does not react normally. 
People begin to laugh and are stifled; they do not get the reinforcement of the 
complete audience. As a result, the audience does not laugh as much as they 
normally would, and they lose part of the enjoyment of the show. It is our feel- 



July, 1940] AUDIENCE NOISE 57 

ing that group laughter contributes to the pleasure and enjoyment of motion 
picture entertainment. 

MR. FRIEDL: In other words, it is not how much one personally enjoys it, but 
how much the other fellow is enjoying it, which also stimulates one to enjoy it 
more. As Mr. Kellogg stated, we may require optimum reverberation limits to 
reduce the noise and increase the volume range; and not get so much out of the 
laughs but rather more enjoyment and relaxation. 

What we are trying to deliver to the audience is a complex thing enjoying 
dialog and a good volume range and a good play, and not just the laughter or 
noise of the theater. 

MR. RYDER: The pleasure of the audience is what we are after, and while 
my reaction follows the reaction of our production group, we may all be in error. 
They have a very definite reaction against any house in which the audience does 
not feel free to laugh. It is surprising how a dead room tends to prevent laughter. 
Our thought in this regard has been substantiated by the preview cards which we 
receive from the various theaters. 

In the case of the Santa Barbara theater, we were able to obtain a normal audi- 
ence reaction prior to the acoustic treatment even though the house had a bad 
echo. Subsequently to the deadening we took pictures to the house and obtained 
a lifeless reaction from the audience, after which the same pictures were taken 
to other theaters where we obtained a normal reaction. 

MR. KELLOGG: Mr. Ryder has brought out a very interesting point about the 
stifling effect of too much sound absorption on audience reaction. It seems clear 
to me, now that he has mentioned it, that the expedient I proposed for reducing 
audience noise could do much more harm than good. 

MR. ROBERTS: I do not believe a low degree of audience noise is objection- 
able, because we become accustomed to it. It is annoying for me to go into a 
theater where there is a high degree of noise, after being accustomed to the 
silence of review rooms. Perhaps, everyone could be conditioned to a low noise 
level in the theater. 

MR. McNABB: There is a great difference among people with regard to the 
level at which they like to listen to music or dialog. For instance, a man who 
works in a noisy factory will, when he returns home at night, adjust his radio to 
a level much higher than his wife would like to listen to, because she is used to the 
quietness of the home. If the majority of theatergoers live in noisy cities, we 
must adjust to a higher level to satisfy them. If the majority of listeners are 
people who live in quiet surroundings, it means that we should have a lower 
level. 

MR. RYDER: There is a difference between audiences in that regard. A tired 
audience such as is encountered in an industrial section such as Whittier or south- 
east Los Angeles will react differently than a Beverly Hills, Westwood, or Pasadena 
audience. Apparently it takes more volume for a tired audience. 

Nerve strain is another thing that affects hearing, a fact that has been recog- 
nized for some time. A director or producer going to a preview is always under a 
strain, which frequently affects his hearing. 

MR. SEELEY: There is also a big difference in auditoriums. The absorption 
is no doubt an important factor, and I rather imagine that the shaping factors 
are very important. That would seem to indicate that the ideal type of volume 



58 W. A. MUELLER 

expansion would, if such a thing were possible, be adjustable to the individual 
house, and perhaps to the individual audience. For example, on Saturday 
afternoon, when the children are in the theater, it would be different from 
what would be required at other times. 

MR. HOVER: Those who work with audiences of 6000 to 10,000 persons often 
are unable to drop the noise level of the audience sufficiently so that their equip- 
ment will work well. The usual system is to drop the gain gradually to the point 
where the audience will have to be quiet to hear the speaker. That works only 
so far, however, because as soon as the audience misses one or two words, im- 
mediately the noise level goes up. The psychological hold on the audience has 
been lost. 

MR. McNABB: Loud entrance music automatically raises the level to which 
people want to listen, and is usually too loud. If the entrance music level were 
kept low, it would tend to keep the audience quieter. 

MR. RYDER: There is a great deal of controversy in Hollywood as to the 
proper volume for main and end titles. It is somewhat like the newsreel problem, 
where each is trying to outdo the other, with no thought of getting into direct 
competition. 

MR. BATSEL: Mr. Mueller's point, I believe, was that compression aids intel- 
ligibility in the presence of noise. That has been confirmed by experience in the 
use of announcing systems in industrial establishments and other places where 
there is noise to contend with. 

MR. SEELEY: A person seems to be more annoyed by a noise that he does not 
quite know, or the presence of which he is not sure, as well as the fact that the 
noise may not be justified. For instance, a person walking down the aisle is 
not quite so annoying as one who is opening a box of candy in the next seat. Those 
factors I think should be considered. 

MR. RYDER: That ties in with the thought that the tests made here were 
monaural as compared with binoral listening. All our sound, including disturbing 
noises, comes from the screen, a point-source. If the audience is listening to sound 
from that source (the screen) and disturbing sounds also come from there, the 
disturbing sounds are much more objectionable than if they are introduced off to 
the side, where the audience can discriminate against them. 



PARTIAL DEAFNESS AND HEARING-AID DESIGN* 

I. CHARACTERISTICS OF HEARING LOSS IN VARIOUS TYPES OF 

DEAFNESS 



WILLIS C. BEASLEY*' 



Summary. This paper deals with certain aspects of the intricate relationship be- 
tween the nature of hearing loss associated with various stages of impairment for 
hearing speech in everyday situations and the possibilities of improving physical 
therapy for the deafened through improvements in the design of hearing aids. 

The data, upon which the study is based, were obtained during a clinical study of 
deafness and aural disease conducted by the United States Public Health Service 
during the spring and summer of 1936. 

Variations in the nature of hearing loss are shown for persons having the following 
stages of practical handicaps for hearing speech in everyday situations: (a) impair- 
ment for hearing at church, in the theater, and in group conversation; (6) impairment 
for hearing conversation at close range; (c) impairment for hearing over the telephone; 
and (d) inability to hear speech under any circumstances. 

Students of physical therapy f for the deafened have observed for 
many years that only a small percentage of hard-of-hearing persons 
who actually try out portable electrical hearing aids regard them as 
being sufficiently helpful to justify the expense and annoyance in- 
volved in using them. Moreover, it has been estimated from a 
recent survey of deafness in the general population that hearing aids 

* Presented at the 1940 Spring Meeting at Atlantic City, N. J. 
** United States Public Health Service, Division of Public Health Methods, 
National Institute of Health, Bethesda, Md. 

t Therapeutics, in the general sense, is the practical branch of medicine dealing 
with the curative treatment of disease. Physical therapy, which is only one small 
phase of the broad field of medical therapy, deals with the prescription of artifi- 
cial devices for curative or rectifying treatment of disease or physical impair- 
ments. Physical therapy for the deafened is limited almost entirely to the 
measurement of auditory acuity (by audiometers or other means) and the pre- 
scription of rectifying hearing aids. This field of physical therapy is in its in- 
fancy, and is in urgent need of systematic information. It is one purpose of this 
discussion to point out some of the unexplored areas where knowledge that is 
indispensable to progress is lacking. 

59 



60 W. C. BEASLEY [J. S. M. P. E. 

of any type are being used by only 5 per cent of the persons who are 
sufficiently hard of hearing to derive benefit from them.* This 
proportion is significantly lower than that which exists for the use of 
physical therapeutic devices in relation to other handicaps, for ex- 
ample, crippled limbs or defective vision. It is clear, therefore, that a 
real problem, which has not been solved, exists in connection with the 
prescription, design, manufacture, and distribution of auricles.** 

Even in the recent past, the view has been expressed widely that 
this limited use of auricles is due largely to mental factors peculiar 
to persons who are hard of hearing, especially their unwillingness to 
accept this type of therapy and their impatience in learning how to 
utilize the artificial aid to best advantage. It is said also that deaf- 
ened persons expect more from auricles than the best engineering 
practice can possibly supply in light, portable (wearable) equipment 
at any price. On the other hand, many physicians and acoustical 
engineers alike are convinced that the appalling failure of this thera- 
peutic service may be ascribed most properly to the fact that auricles, 
either of the vacuum-tube or carbon type, provide grossly inadequate 
corrections of auditory defects as they occur among most patients who 
seek amelioration of this handicap. And, finally, despite the gradual 
but continuous improvement in the performance characteristics of 
auricles during the past fifteen years, the available products are far 
short of what may be viewed as most desirable. 

The testimony of hard-of-hearing patients should not be ignored 
in this prospectus. The writer has interviewed well over a thousand 
clinical patients in connection with the problem of auricles. While 
they present by no means a uniform front in regard to attitudes about 

* This estimate is based on data obtained from the National Health Survey, 
which was conducted in 84 urban areas of the United States during the fall of 
1935 and the winter and spring of 1936. 

** The term "auricle" will be used in this study in the broad sense of any type of 
electrical hearing aid which is sufficiently light to be worn on the person without 
accessory equipment being required. The device is composed typically of the 
following units: microphone; amplifier unit, with volume control ; either an air- 
or bone-conduction receiver; and power supply (usually dry-cell batteries). 
In addition to auricles, semi-portable hearing aids, which are larger and require 
separate carrying cases, and group hearing aids, which are used in churches, 
schools, and theaters, are now in use and are available commercially. An auricle 
may be considered as a device that is intended to correct defective hearing some- 
what in the manner that spectacles are employed to compensate for defective 
vision. The therapeutic problems, however, as will be pointed out later in this 
discussion, are entirely different in regard to auricles and spectacles. 



July, 1940] PARTIAL DEAFNESS AND HEARING AIDS 61 

hearing aids, some views occur much more often than others. The 
numerous reasons, which are usually given in the clinical history, as 
to why individuals reject or even refuse to try out hearing aids may 
be classified suitably under three headings : personal pride, prohibitive 
cost, and poor performance. It is true that some people do not wear 
hearing aids for the sake of personal pride. There is serious objec- 
tion to advertising one's defect by wearing "the crutch" in plain sight. 
Such attitudes are infrequent and are rapidly becoming more so. 
This is easily understood. Persons with any type of handicap soon 
are forced to accept the fact of its existence, and are not only willing 
but anxious to secure remedial treatment, even when the latter re- 
quires wearing a device of one sort or another. 

Prohibitive cost and poor performance are given about equally 
often as reasons for rejecting hearing aids. And these two reasons, 
separately or combined, express the attitude of more than 90 per cent 
of hard-of -hearing persons who have not bought hearing aids for them- 
selves. There is a measure of interdependence, however, between 
these reasons. Hearing aids are in disrepute among hard-of -hearing 
persons. So many people have found them unsatisfactory that others 
who are contemplating trying them out are discouraged by either 
first-hand or second-hand reports. The best salesman is a product 
that perpetually reaches satisfied consumers. 

In this connection, attention is invited to the fact that deafness 
courts both economic and social hazards. Deafness increases unem- 
ployment risk.* Deafness discourages free and spontaneous social 
communication. Hard-of -hearing persons soon learn the force of 
these two facts. They seek to remove both handicaps by every avail- 
able means. Satisfactory performance of auricles is bound, there- 
fore, to outweigh purchase price in the final analysis. Persons who 
are handicapped by impaired hearing want, and one may add, des- 
perately, an auricle which will assist them materially in their jobs 
and in their daily living. Driven by almost reckless desire for allevia- 
tion, they often accept less than worthless devices which soon are 



* During the depression and the immediate sequel thereto, hard-of-hearing 
persons lost their jobs from two to three times more often than persons with 
normal hearing in the same occupational groups. Partial deafness proved to be a 
greater employment liability for professional and business persons than for 
unskilled workers. These facts were disclosed by as yet unpublished results from 
the National Health Survey. 



62 W. C. BEASLEY fj. s. M. p. E. 

discarded. When better auricles are available, undoubtedly there 
will be fewer complaints about purchase price and appearance. 

To some extent, at least, it is expected that performance charac- 
teristics of auricles and their retail price should be directly related. 
However, at present there are only a few manufacturing concerns with 
sufficient volume of business to put auricles of high-quality construc- 
tion (according to present standards) on the market at a reasonable 
price. On the other hand, there is a large number of small-scale 
manufacturers who distribute auricles of definitely inferior grade at a 
price which competes with the better products. The operations of 
these smaller firms constitute a definite hindrance to systematic prog- 
ress, inasmuch as they contribute mainly to enlarging the field of 
dissatisfied customers. But even the most expensive and best con- 
structed auricles from the standpoint of mechanical ruggedness and 
high-quality materials do not solve in even an approximately satis- 
factory manner the problem of aural rectification. This is borne out 
by the large proportion of deafened persons who give them fair trial 
but find them to be of little benefit. 

The major obstacles to providing immediately better service in the 
field of physical therapy for the deafened than that which is now 
available apparently overlap into several fields of science and prac- 
tical effort. The first steps in removing these barriers consist in 
carrying out a coordinated research program that will provide the 
following : 

(1) Extensive information on the fundamental psychophysical 
properties of deafened ears, especially in regard to the perception of 
tones and speech sounds at optimal levels above threshold intensities. 

(2) Development of reliable statistics on the prevalence and dis- 
tribution of various types and stages of deafness in the general popula- 
tion. 

(3) Specifications for the response -frequency and other functional 
characteristics of sound amplifiers that will compensate most ade- 
quately for different patterns and degrees of hearing loss. 

(4) New circuit designs and new functional parts that will enable 
engineers to provide the desired optimal and selective amplification 
in the form of wearable and relatively inexpensive auricles. 

(5) Simplified, standardized, and reliable diagnostic and aural 
testing procedures that will enable the physician, or his technical 
assistant, to derive from the results of an examination a prescription 
for the most beneficial type of auricle for an individual patient. 



July, 1940] PARTIAL DEAFNESS AND HEARING AIDS 63 

(6) Means by which the patient can obtain a reliable fitting in 
accordance with standardized practice once the proper prescription 
has been provided. 

(7) Means by which the patient can be taught properly how to 
use the auricle to best advantage and obtain periodic recheck examina- 
tions. 

(8) Means for controlling the manufacture of auricles, so that they 
must be certified as being in accordance with adopted standards. 
The basis for standardization can be accomplished through the infor- 
mation described under items 1, 2, 3, and 4 above. 

Not until adequate knowledge of this type becomes available can 
any certain steps be taken in the direction of standardizing auricles 
or improving the service to patients. It is possible, of course, even 
when the requisite information is available for writing optimal pre- 
scriptions for auricles that the specifications can not be incorporated 
into the desired wearable auricle by any known engineering technics 
and products. Nevertheless, knowledge on the nature of deafness 
itself is the basis for defining just what the engineer's problem con- 
sists in. 

The present series of papers is intended to provide a contribution 
to one small, but fundamental, phase of this rather involved problem : 
namely, data which show the nature of hearing losses associated with 
several degrees of practical handicaps in hearing speech under every- 
day situations, and the relative frequency of occurrence of various 
patterns of hearing loss. The discussion in the first paper is confined 
largely to a description of the patterns of hearing loss in relation to 
degree of handicap for hearing speech. The second paper in this se- 
ries will deal with statistical estimates on the prevalence of the various 
types of hearing loss in the general population in urban areas of the 
United States. It is thought that data of this type should provide a 
basis for determining characteristics for hearing aids that are needed 
most often. 

THE MEASUREMENT OF AUDITORY ACUITY 

There are many ways of describing, classifying, diagnosing, and 
measuring deafness or loss of normal hearing. During the latter half 
of the nineteenth century, deafness was measured mainly by the 
following methods: (a) the maximum distance at which spoken or 
whispered words could be understood, (b) the highest pitch of a 
tuning fork that could be heard at all, and (c) the maximum time a 



64 



W. C. BEASLEY 



[J. S. M. P. E. 



vibrating tuning fork could be heard when held about half an inch 
from the opening of the ear canal (ah* conduction) or when the stem 
was pressed against a mastoid process (bone conduction). With 
the advent of various methods for generating alternating current, the 
technic known now as "audiometry" was introduced for the purpose 
of measuring in physical units the acuity of hearing for pure tones. 




LEVEL OF PAINFULLY \ 
LOUD TONES FOR 

NORMAL EARS ^ 



LEGEND MEDIAN 

0-90 CENTILE RANGE 



256 512 1024 2O48 4O96 8192 

FREQUENCY IN CYCLES PER SECOND 



FIG. 1. Audiogram chart showing characteristic ranges of 
auditory acuity by air and bone conduction for 1663 persons whose 
hearing is normal in all respects. 



There are several types of audiometers available commercially, 
but most of them given reasonably comparable results when proper 
attention has been given to the zero calibration of the instruments 
and to the characteristics of the receivers. The data upon which the 
present study is based were obtained with the Western Electric 2A 
audiometer. This instrument provides an output of eight pure tones 
spaced at octave intervals from 64 to 8192 cycles per second, over the 
intensity ranges indicated in Fig. 1. The vertical ordinates on this 
chart indicate the frequency level of sound, and the horizontal ordi- 
nates mark off levels of sound intensity relative to a normal average 



July, 1940] PARTIAL DEAFNESS AND HEARING AIDS 65 

zero reference. Negative values on this scale indicate better than 
average normal acuity, and positive values indicate loss of acuity. 

Two types of receivers were used with this audiometer: (a) for 
air conduction the Western Electric Type 55 2 W receiver, and (b) 
for bone conduction the Type 700B receiver. The ranges of hearing 
loss for both air- and bone-conduction measurements obtained for 
1663 persons having normal auditory acuity are shown by the shaded 
areas (Fig. 1).* The median hearing loss for this group is indicated 
by the heavy line near the middle of the shaded areas. Hearing losses 
in Figs. 2 to 10, inclusive, are given as deviations in decibel units 
from the median values for this normal group. 

The 700B bone-conduction receivers were placed against the mas- 
toid process (bony lump behind the external ear), where they were 
held in place by means of steel spring headbands. These receivers 
are driven by alternating current from the audiometer. Since more 
energy is required to drive the bone-conduction receivers than that 
required for the air-conduction receivers, sufficiently to elicit a just- 
perceptible tone, the normal value for bone-conduction thresholds 
(Fig. 1) is at a greater level of "hearing loss" than that for the normal 
air-conduction thresholds. 

The double bars on the chart indicate the maximum hearing loss 
levels which can be measured by means of the Western Electric 2 A 
audiometer. The dashed line on the lower portion of the chart, 
labelled "total loss of serviceable hearing," indicates the intensity 
levels which produce sounds that are painfully loud to persons with 
normal hearing. This region also indicates approximately the mini- 
mum hearing loss for "absolute" deafness. 

In the testing procedure followed during this study, the operator 
of the instrument presented the patient with a tone that was above 
threshold (except cases whose loss was near to or greater than the 
maximum output of the audiometer). The operator ascertained the 
minimum intensity level at which the patient consistently indicated 
that he heard the test tone. The average value for several readings 
obtained in this manner was used as the final measure of acuity. 
A line connecting the average threshold points (illustrated in Figs. 3, 
5, 7, 9, and 11) gives a profile graph or audiogram of the person's 
acuity. An audiogram shows the extent of deviation of an individual's 

* These measurements were made during a clinical study of hearing, which was 
operated under the direction of the writer in twelve cities during the spring and 
summer of 1936. 



66 W. C. BEASLEY [J. S. M. P. E. 

hearing for the various pure tones relative to the normal standard of 
reference. 

Ordinarily, it is considered that values within 10 db of the aver- 
age or median normal are simply chance variations of measurement 
and may be regarded as normal in all respects. Loss of acuity to the 
extent of 20 db or more indicates defective hearing. The greater the 
amount of hearing loss, of course, the more serious the defect. 

DIAGNOSIS OF LESIONS BY AUDIOMETRIC TECHNIC 

The purpose in using both air- and bone-conduction receivers in 
measuring auditory acuity is to aid the physician in determining 
whether hearing loss by air conduction is accompanied by equivalent 
loss by bone conduction, and to provide clues for the diagnosis of 
nerve deafness. When hearing losses by both methods of measure- 
ment are equivalent to each other, the deafness is called perceptive or 
"nerve deafness" and indicates usually that the defective hearing 
may be attributed to one or more of the following conditions: (a) 
primary degeneration of sensory nerve-endings in the inner ear 
(cochlea), (b) degeneration of acoustic ganglion cells, (c) degeneration 
of afferent nerve fibers in the acoustic nerve, or (d) lesions in the 
central pathways of the brain (temporal lobe, or other loci). In 
rare cases, this type of result may be observed when there are no 
nerve lesions at all, but there is some type of bone-conduction im- 
pedance in excess of the normal condition. Diagnosis of nerve lesions 
by this method alone is not absolutely final. 

When there is considerable hearing loss by air conduction, but the 
bone-conduction response is normal, the defect of hearing is attrib- 
uted usually to conductive lesions in the middle ear. Some ex- 
amples of conductive lesions are the following: (a) perforated ear- 
drum; (b) retracted malleus and concave drum membrane; (c) 
absence of drum membrane, malleus and incus; (d) adhesions of in- 
jured tissues in the middle ear, which reduce mobility of eardrum and 
ossicles; (e) sclerosis of tissues in the labyrinth and middle ear; (/) 
suppurative discharges at various loci of the middle and inner ear. 

Sometimes a distinction is made between obstructive and conductive 
lesions. For instance, a suppurative occlusion of the middle ear or 
ankylosis of the stapes interferes (obstructs) mechanical transmission 
of air-conducted sounds, whereas under these circumstances bone- 
conduction acuity is better than normal due to a compression action 
within the cochlea. 



July, 1940] PARTIAL DEAFNESS AND HEARING AIDS 67 

Conductive lesions influence the hearing in several ways: (a) 
acuity by air conduction may be reduced on all tones by approxi- 
mately equal amounts, while acuity by bone conduction remains 
normal on all tones, (b) acuity by air conduction may be reduced on all 
tones, but relatively more for tones lower in frequency than 500 cycles, 
while the acuity by bone conduction remains normal for tones higher 
in frequency than 500 cycles but is better than normal for lower 
tones, (c) acuity by both air and bone conduction is reduced on all 
tones, but proportionately more by air conduction on some middle 
and low tones (64 to 512 cycles) and about equally on high tones 
(4096 and 8192 cycles). Such diagnoses can not be accomplished 
with certainty by audiometric technic alone. 

Nerve deafness may influence the hearing for some or all tones, 
conductive lesions may reduce acuity for some tones and not for 
others. In the same ear, moreover, loss of acuity on some tones may 
be due to conductive lesions, and on other tones the loss may be due 
to nerve lesions. In the latter case the deafness is regarded as being 
of a "mixed type." Combined conditions of obstructive, conduc- 
tive, and nerve lesions may exist in the same ear. There are two 
major reasons why it is important to determine the extent to which 
cases of deafness are of the pure nerve type, the pure conductive type, 
the pure obstructive type, or of the mixed type: (a) the prognosis 
for treatment differs for various kinds of lesions, and (b) the hearing 
for sounds well above one's own threshold value varies with the type 
of lesion. Because important pathology may be present in such de- 
gree as to render inadvisable the use of a hearing aid, persons con- 
templating trial of this device should consult a medical specialist 
before deciding. Moreover, measurements by the threshold acuity 
technic alone do not provide accurate predictions for the ability to 
hear sounds well above threshold. The amount and kind of error 
involved in making these predictions differ notably for the various 
types of deafness, depending on the nature and extent of conductive, 
obstructive, and nerve lesions involved. The magnitude of sound 
intensities which the diseased ear can tolerate without pain or serious 
discomfort also varies with the type of deafness and organic condition 
of the ear. 

DEFINITIONS FOR CLINICAL HISTORY OF IMPAIRED HEARING 

Partial deafness may be measured in terms of (a) audiograms show- 
ing loss of acuity by air and bone conduction , (b) loudness contours 



68 W. C. BEASLEY [j. S. M. p. E. 

indicating response to sounds which are well above threshold intensi- 
ties, (c) speech articulation tests, and (d) language intelligibility 
tests. A fifth equally important method for classifying aural handi- 
caps is the clinical history, which utilizes certain explicit definitions 
of auditory experience. The patient's testimony is classified in ac- 
cordance with definitions, which specify gradations in severity of deaf- 
ness in relation to practical situations. Regardless of refinements 
incorporated in instrumental technics, it is ultimately of practical 
importance to know what correlation exists between the results of ob- 
jective tests and the usual experience of the individual in communicat- 
ing with others by vocal-aural transmission. The clinical history 
technic requires, of course, careful attention to the manner of con- 
ducting an interview with the patient, quite as much as audiometric 
technic requires uniform and standardized procedures in conducting 
objective tests of hearing. And the results from both methods are 
equally useful when appropriate limitations are imposed on inter- 
pretation of results obtained by either technic. 

In the spring and summer of 1936, the United States Public Health 
Service conducted a clinical investigation of hearing at 17 temporary 
otological clinics which were operated under the direction of the 
writer. These clinics were located in 12 cities in the eastern half of 
the United States. Audiometric tests and otological examinations 
were given to some 9000 males and females ranging in age from 8 to 90 
years. 

Each clinical patient was interviewed by a physician. A standard 
series of questions was employed during this interview, and each 
patient's experience in regard to his hearing ability was classified 
according to one of the following categories, depending upon which 
definition applied most directly to his case : 

(1 ) Normal Hearing for Speech. The person had never experienced 
difficulty at any time with his hearing. 

(2) Partial Deafness, Stage 1. The person experienced difficulty 
in hearing speech at the theater, in church, or at a conference of 
five or six persons, but could understand direct conversation satis- 
factorily. 

(3) Partial Deafness, Stage 2. The person experienced difficulty 
in hearing ordinary direct conversation, but could hear loud speech, 
telephonic conversation, or speech amplified by other means. 

(4) Partial Deafness, Stage 3. The person experienced difficulty in 
hearing ordinary telephonic conversation, but could hear speech by 



July, 1940] PARTIAL DEAFNESS AND HEARING AIDS 69 

means of amplifiers such as telephone amplifiers, electrical hearing 
aids, etc. 

(5) Total Deafness for Speech. The person could not understand 
speech under any circumstances, even by means of amplifiers, but the 
impairment was acquired after the person had learned to speak lan- 
guage by ordinary methods of training. 

(6) Deaf -Mute. The person was born deaf or acquired severe 
deafness at such an early age that he did not learn to speak language 
by ordinary means. 

During this clinical investigation, measurements of auditory acuity 
were taken on eight tones by air conduction and six tones by bone 
conduction with Western Electric 2 A audiometers and their associated 
receivers. All instruments and receivers were calibrated prior to, 
during, and after the survey by expert technicians of the Bell Tele- 
phone Laboratories. Measurements were taken in specially con- 
structed sound-insulated booths. Thorough oto-rhino-laryngological 
examinations were made on each subject and extensive medical his- 
tories and personal data were obtained in addition to the clinical his- 
tory of auditory experience. 

CHARACTERISTIC TRENDS IN ACUITY 

For the purposes of this study, the measurements of auditory 
acuity were classified in groups according to the clinical history of 
hearing ability separately for all females under 25 years of age, and 
for all males 45 years of age and over. All the measurements on 
each test tone, for example, were classified in tabular form showing the 
number of measurements at each setting of the audiometer intensity 
control. Such an array of data is referred to as a frequency dis- 
tribution. The hearing loss level was computed, in accordance with 
standard statistical procedure, for each of the following percentages 
of the total number of measurements in a given frequency distribu- 
tion: 10, 25, 50, 75, and 90 per cent. The computed hearing loss 
values at each of these percentage levels were employed in plotting 
the graphs shown in Figs. 2, 4, 6, 8, and 10. 

The graphic contours, which result from connecting the points for a 
given percentage value, will be referred to conveniently as "percentage 
audiograms." Thus, the family of percentage audiograms for all 
females under 25 years of age having a clinical history of normal 
hearing is illustrated in Fig. 2A. The contour labelled "10 per cent" 
at the right indicates the hearing loss level on the seven test tones at 



70 W. C. BEASLEY [j. s. M. P. E. 

which, cumulatively from the lowest values (least hearing loss) in the 
frequency distribution, 10 per cent of the measurements occur. In a 
similar way, the other percentage audiograms indicate in graphic 
form the hearing loss levels at which specified percentages of mea- 
surements, relative to the most sensitive ear, occur for each group of 
subjects. 

These contours may be regarded as depicting statistical trends for a 
group, not as representing a hypothetical average person. In general, 
the scalar distances between the percentage points on each ordinate 
give an estimate of the dispersion of measurements in relation to the 
centra] tendency, which is indicated by the median value (50 per 
cent contour). Instances in which the distances between these per- 
centage points are relatively longer indicate greater variability in the 
relationship between hearing loss, or measurement of acuity, and the 
testimony of the patient in regard to his auditory experience, when 
the latter is classified according to the clinical history definitions given 
above. By comparing these distances between the points for indi- 
vidual tones in a family of contours for a given clinical history, one 
may draw conclusions regarding the extent to which indicated ranges 
of hearing loss are more critically related to some tones than to others 
for that type of auditory experience. Comparisons of this type are 
made below in relation to each group. 

In cases where the distances between these percentage points are 
approximately equal for a given frequency distribution, the measure- 
ments tend to be symmetrically distributed about the median value. 
Two other features of the frequency distributions enter into the discus- 
sion : positive and negative skewness. When the distances of the 75 
and 90 per cent points from the median (50 per cent point) are greater 
than the distances of the 25 and 10 per cent points from the median, 
the distribution of measurements is skewed positively. In such cases 
there is a definite trend for deviations from the median in one direction 
(greater hearing loss) to be larger in value than those in the opposite 
direction. When skewness is the reverse of this type, the distribution 
of measurements is said to be negatively skewed. Interpretation of 
statistical trends shown by the various families of percentage audio- 
grams should take into account the degrees of dispersion, as well as the 
sign and magnitude of skewness, for distributions of measurements on 
the various tones. 

The central 50 per cent of the measurements for each family of 
percentage audiograms is indicated by the distance between the 25 



July, 1940] PARTIAL DEAFNESS AND HEARING AIDS 71 

and 75 per cent audiograms. It is believed that this area may be re- 
garded as the most characteristic range of hearing loss that is asso- 
ciated with a given type of clinical history. 

NORMAL HEARING FOR SPEECH 

Characteristic ranges of hearing loss found among persons having a 
clinical history of normal hearing for speech are shown by the per- 
centage audiograms in Fig. 2. The most frequent types of individual 
cases usually encountered among males and females in three broad 
age groups (under 25 years, between 25 and 45 years, and 45 years of 
age and over) are illustrated by the audiograms in Fig. 3. 

More than 90 per cent of the females under 25 years of age have 
normal audiograms for both air and bone conduction. Males 45 
years of age and over have normal audiograms in less than 30 per cent 
of the cases. The type of defect which occurs most often among the 
older males, and to a lesser extent among older females, consists in 
nerve lesions involving loss of acuity for the two highest tones. 
This hearing loss is of such a character, however, that the persons 
have very little difficulty hearing tones or speech sounds that are 
60 or more db above normal threshold intensity. Hence, they are 
unaware of the defect before it has been disclosed by audiometric 
technic. 

STAGE 1 DEAFNESS 

Cases of stage 1 deafness are of considerable importance, although 
there has been a tendency to disregard them, especially in relation to 
the problem of hearing aids. In accordance with the definition, stage 
1 deafness includes impairment for distant speech, such as that en- 
countered at the theater, in church, and in other public auditoriums 
as well as during group conferences. Although the handicap itself is 
somewhat manageable, the degrees of hearing loss associated with this 
stage of deafness are sufficient to warrant the use of properly designed 
hearing aids. From a technical standpoint, the types of hearing aid 
which would serve these patients well should be a fairly simple matter 
for the engineer. Hearing aids themselves are not sufficiently popu- 
lar at the present time to attract the attention of persons having a 
degree of handicap indicated by stage 1 deafness. If the custom of 
using hearing aids were considerably more widespread than at present, 
there is little doubt that a large number of people in the stage 1 deaf- 



72 



W. C. BEASLEY 



IJ. S. M. P. E. 



ness group would be inclined to use a hearing aid for certain occa- 
sions in which they now experience their major difficulties. 

Persons with this type of impairment would derive quite as much 
practical benefit through the use of suitably designed hearing aids as 
persons with minor degrees of astigmatism, hyperopia, or myopia 
derive from properly determined lens corrections. Just as persons 



NORMAL HEARING FOR SPEECH 



FEMALES : UNDER 25 YEARS 



MALES :45 YEARS AND OVER 



MAX. OUTPUT 
Or AUDIOME 



TER\ 



MAX. OUTPUT ___ 

OF AUDIOMETER" 



CONDUCTION 



BONE 
CONDUCTION 




126 256 512 1024 2048 4096 8192 



128 256 512 1024 2048 4096 8192 
_ES PER SECOND 



FIG. 2. Percentage audiograms showing characteristic ranges of hearing 
loss by air and bone conduction for females under 25 years of age, and males 
45 years of age and over, having a clinical history of normal hearing for 
speech. 

with minor visual defects manage to get along under most visual cir- 
cumstances without spectacles, so persons with stage 1 deafness man- 
age to get along without artificial hearing devices. However, there 
are numerous situations in which people with stage 1 deafness would 
benefit appreciably if they could produce at will a gain of some 20 or 
30 decibels in the intensity level of received speech, or could amplify 
differentially the higher frequencies in the received speech without 
altering the middle and low frequencies. 



July, 1940] PARTIAL DEAFNESS AND HEARING AIDS 



73 



The families of percentage audiograms illustrated in Fig. 4 show 
the ranges of hearing loss that characterize stage 1 deafness as it oc- 



NORMAL HEARING FOR SPEECH : AIR BETTER EAR <-o WORSE EAR 




FIG. 3. Individual cases illustrating the various types of hearing losses 
which occur among persons having no noticeable difficulty with hearing. 



curs among females under 25 years of age and males 45 years of age 
and over. Individual cases are illustrated in Fig. 5. The percentage 



74 



W. C. BEASLEY 



[J. S. M. p. E. 



audiograms for females cover a rather wide range of hearing loss on 
each tone, but the fact that these percentage audiograms are approxi- 
mately parallel is consistent with the fact that the individual audio- 
grams of the persons included in this tabulation are most frequently 
horizontal. On the other hand, the audiograms for males (Fig. 4J3) 
are parallel but each contour slopes gradually from left to right on the 




FIG. 4. Percentage audiograms showing characteristic ranges of hearing 
loss by air and bone conduction for females under 25 years of age, and males 
45 years of age and over, having a clinical history of stage 1 deafness. 



chart. The whole family of audiograms for males shows approxi- 
mately 15 db less loss than that for females on tones below 1024 
cycles, whereas for tones above 1024 cycles the family of curves for 
males shows uniformly a hearing loss 20 decibels greater than that for 
females. It will be noted that the measurements for females on the 
three highest tones show relatively greater loss for tones below 1024 
cycles than for tones above this level in 50 per cent of the cases. 
About 35 per cent of the audiograms in this group show a slight but 



July, 1940] PARTIAL DEAFNESS AND HEARING AIDS 



75 



gradually increasing loss from low to high tones. The former trend 
is typical for deafness cases in which the impairment is due almost 




512 1024 204 



FREQUENCY IN CYCLES P.CR SECOND 



FIG. 5. Individual cases illustrating the various types of hearing losses 
which occur in stage 1 deafness. 

entirely to conductive lesions in the middle ear. A further indication 
that these cases predominate among females under 25 years of age is 



76 W. C. BEASLEY [j. S. M. P. E. 

revealed by the nature of the percentage audiograms for bone con- 
duction in Fig. 4C. There are relatively more cases of bone-conduc- 
tion acuity at better than normal levels than are found among per- 
sons with normal hearing. On the other hand, the higher tones do not 
show a similar influence from conductive deafness. It appears that 
the vast majority of stage 1 deafness cases among females under 25 
years of age may be considered as arising from conductive lesions, 
with relatively little nerve degeneration and involving typically a 
uniform hearing loss for all tones to the extent of 20 to 30 db by air 
conduction and no significant loss for bone conduction. Hearing 
aids which employ air-conduction receivers would be best suited to 
these persons, if they were capable of producing faithful amplifica- 
tion over the range 500 to 4000 cycles to the extent of about 25 db. 
Bone-conduction receivers which render speech intelligible to persons 
with normal hearing would also be suitable in the majority of cases. 
On the other hand, uniform amplification would probably not serve 
as well in improving the hearing of males 45 years of age and over. 
These cases typically show relatively greater loss for tones in the 
upper register for both air and bone conduction. This means that the 
impairment involved in stage 1 deafness among older males typically 
arises from nerve degeneration. Hearing loss of this type can not be 
rectified by means of artificial amplification in the same manner as im- 
pairments arising from conductive lesions. For the typical case in 
this group there is normal bone-conduction acuity for tones from 64 
up to 512 cycles. For the higher tones, bone-conduction acuity is 
greatly reduced. A hearing aid which employs a bone-conduction 
receiver will rectify this type of auditory impairment satisfactorily 
if it supplies a differential gain in relation to frequency such that a 
person with this type of loss hears all tones with approximately normal 
loudness when the sounds external to the hearing-aid microphone are 
at intensities usually employed in speech. This type of hearing aid 
would have to produce zero gain for tones below 1000 cycles and 
about 35-db gain for tones above 3000 cycles, with proportionate gain 
between 1000 and 3000 cycles. On the other hand, a hearing aid 
which employs an air-conduction receiver would have to produce a 
gain of about 20 db for sounds below 1000 cycles and gradually in- 
creasing gain for sounds above 1000 cycles, reaching a maximum level 
of about 50-db gain at 4000 to 6000 cycles. These statements assume, 
of course, that the hearing aid is employed to remove the type of 
hearing difficulty reported upon by the patient. In cases of stage 1 



July, 1940] PARTIAL DEAFNESS AND HEARING AIDS 77 

deafness, this means difficulty in hearing speech in public auditoriums, 
in church, at the theater, and in group conferences. In such circum- 
stances, sound intensities at the ear of the listener will vary greatly 
depending upon the speakers, the distance between the speaker 
and the listener, the amount of background noise, and the acoustical 
properties of the auditorium. It is probably safe to say that the 
average level above threshold for all these varying conditions at the 
ear of the listener will be about 40 to 50 decibels. Steinberg and 
Gardner's curves indicate that at this level, persons having a nerve 
deafness type of impairment recover only about 50 per cent of normal 
loudness. 

STAGE 2 DEAFNESS 

Cases classified under stage 2 deafness comprise those who ex- 
perience difficulty understanding ordinary conversation at close range. 
For the most part, these persons can not hear at all in public audi- 
toriums and similar situations in which the speech level at the ear of 
the listener is usually 50 decibels or less. Some of these cases can 
hear exceptionally well direct conversation uttered close to the ear, 
or can understand speech which has been amplified. Although there 
are quite a number of cases in this classification who would be ex- 
pected to hear reasonably well over the telephone, there are many 
who could not do so without considerable amplification, such as that 
supplied at the present time by telephone companies for the private 
consumer's use. 

By way of illustrating the amounts of hearing loss typically in- 
volved in stage 2 deafness among extremely different cases, percent- 
age audiograms for females under 25 years of age and for males 45 
years of age and over are depicted in Fig. 6. Typical cases for males 
and females of various ages having markedly different etiology are 
shown in Fig. 7. Among females under 25 years of age, more than 
50 per cent of the hearing loss measurements for air conduction are 
distributed within the range 40 to 60 decibels. About 90 per cent 
of the measurements for tones above 500 cycles are distributed be- 
tween 35 and 70 decibels. It is to be noted that measurements on 
128 and 256 cycles cover a much wider range of hearing loss than 
those on the other tones. This means, of course, that the degree of 
hearing loss on these two tones does not influence ability to hear 
speech as much as the degree of hearing loss on higher tones. Sec- 
ondly, that even at these marked levels of hearing loss there is a 
definite tendency for the amount of loss on the middle and high tones 



78 



W. C. BEASLEY 



[J. S. M. P. E. 



to exceed that on the lower tones. This kind of trend predominates 
and characterizes the measurements among males 45 years of age 
and over who have stage 2 deafness. As shown in Fig. QB, 50 per 
cent of the measurements on the males for 128 and 256 cycles are less 
than 30 decibels, whereas on 1024 and 2048 cycles more than 50 per 
cent of the measurements are in excess of 50 decibels. 




FIG. 6. Percentage audiograms showing characteristic ranges of hearing 
loss by ah* and bone conduction for females under 25 years of age, and males 
45 years of age and over, having a clinical history of stage 2 deafness. 

A trend similar to that shown for stage 1 deafness is again shown 
for stage 2 deafness. Females tend to have a fairly uniform hearing 
loss on all tones by air conduction ; males have progressively increas- 
ing degrees of hearing loss from low to high tones. Cases of stage 2 
deafness, for the most part, represent a loss of about 50 per cent 
of the total normal hearing capacity. 

The problem of residual hearing is not acute for these cases. How- 
ever, because of the fact that there is such a wide variety of hearing 



July, 1940] PARTIAL DEAFNESS AND HEARING AIDS 



79 



loss patterns which yield a degree of practical handicap correspond- 
ing to the definition of stage 2 deafness, it is an extremely difficult 



STAGE 2 DEAFNESS: AIR CONDUCTION BETTER EAR o--o WORSE EAR BONE 3 




FREQUENCY IN CYCLES PER SECOND 



FIG. 7. Individual cases illustrating the various types of hearing losses 
which occur in stage 2 deafness. 

problem to design hearing aids which can rectify all these defects. 
For the typical female having stage 2 deafness, a hearing aid which 



80 W. C. BEASLEY [j. s. M. P. E. 

gives uniform amplification to sounds above 500 cycles would give 
highly satisfactory results if the total gain were 35 to 40 db. For a 
typical male 45 years of age or over having stage 2 deafness, the am- 
plification gain should be relatively greater for sounds above 1000 
cycles and relatively less for sounds below 1000 cycles. The total 
gain must be somewhat more than in the case of the females and the 
necessity for eliminating background noises of low frequency is more 
important, since in most cases these patients have fairly acute hear- 
ing for all sounds from 64 cycles up to 256 cycles. Inasmuch as these 
frequencies play no part in speech articulation, they should be elimi- 
nated in the circuit. 

Comparison of Figs. 6^4 and 6C leads to the conclusion that cases of 
stage 2 deafness among females under 25 years of age are of two gen- 
eral types: one being essentially a conductive loss ranging from 25 
to 45 db by air conduction, with normal acuity by bone conduction; 
and the second being a uniform type of nerve deafness where the loss 
by air conduction is in the neighborhood of 50 to 60 db, accompanied 
by an equivalent loss by bone conduction. A third type, not as prev- 
alent as <these two, involves a loss which characterizes males 45 
years of age and over. On the other hand, by comparing Figs. 6^4 
and 6B it is seen clearly that stage 2 deafness among males is fairly 
homogeneous in type, involving marked nerve deafness of the chronic 
progressive type. Less than 25 per cent of the males have any us- 
able hearing by bone conduction for tones higher in frequency than 
1000 cycles, whereas more than 75 per cent of the females have 
fairly good hearing by bone conduction on these frequencies. 

STAGE 3 DEAFNESS 

Cases of deafness in which the impairment is sufficiently severe to 
prevent perception of speech over the telephone are classified under 
stage 3 deafness. The majority of persons included in this group have 
sufficient residual hearing to understand loudly spoken words or 
speech which has been amplified by artificial means. This degree of 
impairment is a serious handicap to any kind of employment in which 
hearing is even a secondary matter and prevents the individual from 
enjoying music, drama, sound motion pictures, and direct conversa- 
tion with one or more persons. There are no portable hearing aids on 
the market at the present time which even approximately satisfy the 
requirements of most cases of stage 3 deafness. There are several 
models of nonportable equipment which give definitely satisfactory 



July, 1940] PARTIAL DEAFNESS AND HEARING AIDS 81 

performance for some cases of stage 3 deafness. The major difficulty 
in the way of providing satisfactory portable sets for these persons 
appears to lie in the large amount of power required and the intricacy 
and, hence, bulk of the necessary circuit parts that will produce proper 
selective amplification. As a group, these persons manifest con- 
siderable anxiety because they are aware of a highly distorted auditory- 
world and one to which they can not adjust themselves satisfactorily. 
Persons with somewhat greater aural handicap resign themselves 
more easily to a world which excludes auditory perception and have 
less concern about restoring the use of a sensory facility which they 
once enjoyed. Stage 3 deafness cases are still able to hear, but are 
not able to perceive speech to any appreciable extent. 

Characteristic ranges of hearing loss encountered in stage 3 deaf- 
ness are illustrated by the percentage audiograms in Fig. B. Repre- 
sentative individual cases are shown in Fig. 9. Fig. 8-4 shows that 
more than 85 per cent of the measurements on females under 25 
years of age with stage 3 deafness are at a hearing loss level less than 
80 decibels. About 70 per cent of the measurements lie between 60 
and 80 decibels' loss. Comparison of Figs. 8^4 and SB reveals that 
the ranges of hearing loss occurring in stage 3 deafness are approxi- 
mately the same for females under 25 years of age and males 45 years 
of age and over. A separate tabulation of individual audiograms 
indicates, however, that an age-sex difference similar in type to that 
illustrated above for stages 1 and 2 deafness exists also for stage 3 
deafness, although such differences occur less often at the stage 3 
deafness level. By comparing Figs. 8C and 8D one notes that males 
show retention of good hearing by bone conduction for 256, 512, and 
1024 cycles more often than the females. These differences are 
significant from the standpoint of hearing-aid design, since the type 
of selective amplification that will produce maximal speech articula- 
tion must take into account the relative amounts of residual hearing 
by bone conduction. 

TOTAL DEAFNESS FOR SPEECH 

Total deafness for speech in the present study was defined as "in- 
ability to hear speech under any circumstances, even by means of 
hearing aids or other types of amplifiers." A second qualification 
placed upon the definition was that the impairment was acquired after 
the individual had learned speech in the normal manner. Persons 



82 



W. C. BEASLEY 



[J. S. M. P. E. 



were classified as deaf-mutes if they had acquired severe deafness be- 
fore learning to speak. 

The distributions of hearing loss measurements on females under 
25 years of age and on males 45 years of age and over in the total 
deafness group are illustrated in Fig. 10. The total loss of hearing for 
all tones by either air or bone conduction is greater for the younger 




FIG. 8. Percentage audiograms showing characteristic ranges of hearing 
loss by air and bone conduction for females under 25 years of age, and males 
45 years of age and over, having a clinical history of stage 3 deafness. 

females than for the older males. This difference in character and 
degree of hearing loss is consistent with the age-sex differences shown 
for the three stages of partial deafness. 

The inference is drawn from the nature of the residual hearing 
and from the supplmentary data obtained from the clinical history 
and the otological examinations that the majority of these severe deaf- 
ness cases among the older males are advanced stages of chronic 
progressive nerve deafness, which typically exhibits relatively 
greater losses for the higher tones. 



July, 1940] PARTIAL DEAFNESS AND HEARING AIDS 



83 



Total deafness for speech is more uniform in relation to sound fre- 
quency among young children and adolescents. It is noted that 



STAGE: 3 DEAFNESS : 



UNDER 25 YEARS 



25 TO 44 YEARS 



45 YEARS AND OVER 



Jar 



\ 



\J 



2M SI2 1024 204 4096 256 512 1024 2048 4096 256 512 1024 2048 4096 

racoucNCt IN CYCLCS PC* SECOND 

FIG. 9. Individual cases illustrating the various types of hearing losses 
which occur in stage 3 deafness. 

among the older males hearing loss on tones under 1000 cycles is less 
than 85 db for more than 50 per cent of the cases, whereas for tones 



84 



W. C. BEASLEY 



[j. a M. p. E. 



higher in frequency than 1024 cycles about 90 per cent of the males 
show hearing loss in excess of 80 db. Less than 25 per cent of the 
people in the totally deaf group are actually totally deaf for speech 
sounds, but a much greater power level is required to enable any of 
these people to hear speech with any useful degree of articulation than 
is available in portable hearing-aid sets. An overall gain of about 65 




FIG. 10. Percentage audipgrams showing characteristic ranges of hearing 
loss by air and bone conduction for females under 25 years of age, and males 
45 years of age and over, having a clinical history of total deafness for speech. 

to 70 decibels is required to render the various important components 
of speech sounds sufficiently loud to enable the deafened listener to 
understand 50 to 60 per cent of the speech. There are two additional 
insurmountable difficulties in the way of providing hearing-aid equip- 
ment for persons having this degree of auditory handicap. First, 
normal speech undergoes a wide variation in maximum and minimum 
power levels from moment to moment. These fluctuations in power 
level are essential properties of normal speech sounds. In order for 



July, 1940] PARTIAL DEAFNESS AND HEARING AIDS 85 

the listener to respond to these variations he must have a range of 
serviceable hearing to the extent of about 70 db above his threshold 
values. As the amount of hearing loss increases, the useful range of 
hearing is narrowed so that the greater the degree of hearing loss, the 
more restricted becomes the capacity of the ear to respond to this 
wide range of sound intensities. No type of hearing aid can over- 
come this limiting factor. Secondly, for persons with marked deaf- 
ness, sounds which are barely audible may be painfully intense and, 
hence, the individual can not tolerate continuous stimulation. This 
difficulty can not be overcome in hearing-aid design. It appears, 
therefore, that the question of providing artificial aids to hearing 
for persons having hearing losses in excess of 80 decibels is restricted 
to the possibility of enabling the listener to hear "guiding" sounds, 
rather than complete perception of speech. 

BIBLIOGRAPHY 

BORDLEY, J. E., AND HARDY, M. : "Effect of Lesions of the Tympanic Mem- 
brane on the Hearing Acuity," Archil). Otolaryng., 26 (1937), p. 649. 

CROWE, S. J., GUILD, S. R., AND POLVOGT, L. M.: "Observations on the 
Pathology of High-Tone Deafness," Bull. Johns Hopkins Hosp., No. 54 (1934), p. 
315. 

FLETCHER, H.: "Physical Characteristics of Speech and Music." Bell Sys. 
Tech. Jour. (Oct., 1938), p. 349. 

FLETCHER, H., AND MUNSON, W. A.: "Loudness: Its Definition, Measurement 
and Calculation," Jour. Acous. Soc. Amer., 12 (1933), p. 377. 

FLETCHER, H. : "Hopeful Trends in the Testing of Hearing and in the Pre- 
scribing of Hearing Aids," Proc. Fifteenth Ann. Meeting, Amer. Fed. Org. for the 
Hard of Hearing (1934), p. 116. 

FLETCHER, H., AND MUNSON, W. A.: "Relation Between Loudness and 
Masking," Jour. Acous. Soc. Amer., 9 (1937), p. 1. 

MARTENS, E. H.: "The Deaf and the Hard-of-Hearing in the Occupational 
World," Butt. No. 13, U. S. Dept. of Interior (1937). 

NEWHART, H.: "How the Interests of Otologists, Leagues for the Hard of 
Hearing, and Hearing- Aid Manufacturers Interlock," Proc. Sixteenth Ann. 
Meeting, Amer. Fed. Org. for the Hard of Hearing (1935), p. 16. 

POLVOGT, L. M., AND BORDLEY, J. E.: "Pathologic Changes in the Middle 
Ear of Patients with Normal Hearing and of Patients with a Conduction Type of 
Deafness," Ann. Otol., Rhinol. and Laryng., 45 (1936), p. 760. 

STEINBERG, J. C.: "Effects of Distortion on the Recognition of Speech 
Sounds," Jour. Acous. Soc. Amer., 1 (1929), p. 121. 

STEINBERG, J. C. : "Telephone Research and Problems," Bell Tel. Quart. 
(1936), p. 3. 

STEINBERG, J. C., AND GARDNER, M. B.: "The Dependence of Hearing 
Impairment on Sound Intensity," Jour. Acous. Soc. Amer., 9 (1937), p. 11. 



REPORT OF THE STUDIO LIGHTING COMMITTEE 1 



Summary. A brief survey of some new technics in studio lighting practice, 
covering both carbon arc and incandescent lighting. 



Since the Fall Convention of the Society, studio production has 
been at a relatively low ebb owing to the exigencies of the war situa- 
tion which has had a profound effect upon the motion picture busi- 
ness. There have, however, been some innovations in the technics of 
studio lighting which should be reported. 

RECENT STUDIO INCANDESCENT LIGHTING EQUIPMENT 

(7) An improved 5-kw mogul bipost lamp was introduced using a 
T64 bulb in place of the usual G64. The new shape provides addi- 
tional bulb volume and removes the glass, at the critical point, farther 
from the filament so as to prevent blistering. Along with the tem- 
perature decrease of the bulb, lamp blackening is markedly reduced 
so that the effective life of the lamp is considerably prolonged, es- 
pecially in the case of color-photography CP globes for Technicolor 
use. 

(2) R-40 reflector lamps now available in spotlight and flood- 
light types in both the 150 and 300- watt sizes, as well as a 500- watt 
photoflood type, are being used by some studios where a small but 
efficient floodlight is necessary, such as for close-ups, behind set pieces, 
etc. R-2 reflector photofloods have been used to illuminate the mattes 
for the process shots in some of the outstanding recent color 
photography. 

(3) Daylight fluorescent lamps were introduced to studio lighting 
technic by several progressive cameramen of leading studios. The 
high diffusion, freedom from glare, and coolness of these lamps are 
among the advantages of this equipment, as well as the high actinic 
value which makes the lamps far more effective than the visible effect 
would indicate. 

Tests made by the Eastman Kodak Company indicate that fluores- 
cent lamps have eight to ten times the effectiveness photographically 

* Presented at the 1940 Spring Meeting at Atlantic City, N. J.; received April 
22, 1940. 



STUDIO LIGHTING COMMITTEE REPORT 87 

as the same wattage of studio type incandescent lamps, which indi- 
cates considerable future promise for these sources. 

(4) Newly developed tubular 3, 5, and 7-kw biplane filament pro- 
jection lamps are being used for process projection of still back- 
grounds. In Twentieth Century-Fox's Everything Happens at Night, 
over thirty of the slide backgrounds were illuminated by the 7-kw 
lamp. 

(5) Small spotlights using 100 and 150- watt tubular projection 
lamps were developed by the Warner Bros. Studio. These small 
spotlights, now commercially available, are used for close-up lighting 
and where space is at a premium. 

CARBON ARC LIGHTING 

There have been no basic changes in lamp design, though a number 
of refinements have been made by the manufacturers of such studio 
lighting equipment. 

A 16-mm. X 22-inch super high-intensity studio positive carbon 
has been produced which is capable of burning at currents as high as 
225 amperes and 75 arc volts. This carbon is finding considerable 
use in process projection work where the larger source and higher in- 
trinsic brilliancy is needed for adequate screen illumination. 

LENS TREATMENT 

Surface treatment of camera lenses to increase their transmission 
and to eliminate internal surface reflection is undergoing a stage of 
development and initial application. The advantages gained by such 
lens treatment will undoubtedly in some degree affect the methods of 
studio lighting. Details of this development are reported in a paper 
by W. B. Ray ton, published in this issue of the JOURNAL on p. 89. 

E. C. RICHARDSON, Chairman 

F. E. CARLSON R. E. FARNHAM C. W. HANDLEY 

F. M. FALGE D. B. JOY 

DISCUSSION 

MR. WILLIFORD: Are the new fluorescent tubes operated on alternating or di- 
rect current? 

MR. E. C. RICHARDSON : Both. Basic to the operation of those tubes is a hot 
cathode mercury arc, and since it is an arc, there has to be a ballast medium in the 
circuit. If they operate on direct current the ballast is a resistance, and if they 
operate on alternating current it is a reactance. There is a possibility of operating 
the fluorescent lamp on 3-phase current. With certain of the fluorescent bodies 



88 STUDIO LIGHTING COMMITTEE REPORT 

fortunately there is a delay. The fluorescence does not change much during the 
arc cycle. In some applications three lamps are used, one in each phase of the 
circuit, by which a practically uniform and continuous emanation results. 

The principal objection to the fluorescent lamp at the present stage is that it is 
a "soft," non-pro jectable source. They are good for broadside lighting, and 
might be very useful for lighting backings. But much photographic lighting has 
to be done by projectable sources, and there are new sources coming. At a re- 
cent meeting of the Pacific Coast Section Mr. F. M. Falge of the General Electric 
Company gave us a report and demonstration of a large group of developments 
of his company. About a dozen new lighting mediums, sources and devices, were 
presented, and of the total number not one existed five years ago. 

MR. KELLOGG: How seriously is the 48-cycle lamp being considered? 

MR. RICHARDSON : It is not being considered at all, as far as I know. Its possi- 
bilities have been known for a long time, but we are confronted with the problem 
of bucking the existing standardization. 

MR. HYNDMAN: The Studio Lighting Committee has about two major func- 
tions: One is to report on the progress of studio lighting; and, second, in doing so, 
to recommend procedures, if possible. At the present stage of the lighting art 
recommended procedures of lighting would appear to be very difficult, because one 
has to accept whatever the cameraman believes to be the proper lighting for a 
given artistic effect. Therefore, it does not fall within the scope of the Studio 
Lighting Committee to study the quality of pictures. All it can do is to study the 
conditions, characteristics, and applicability of given light-sources. 

MR. CRABTREE: Is the heat problem still serious in the studios? 

MR. RICHARDSON: The heat problem is practically negligible today; the in- 
creased speed of film has reduced the light intensity in general, and extremely so 
in black-and-white sets. 

The arc lighting for Technicolor pictures has presented no heat difficulties, be- 
cause the spectrum emanation is principally in the shorter wavelengths. 

MR. CRABTREE: Is there any trend away from or toward arc or incandescent 
lighting? 

MR. RICHARDSON: When Technicolor developed the three-color process, back 
in 1933, they started using arc lighting entirely in their photographic operations 
since the carbon arc was a source of illumination that was very close to daylight. 
New equipment had to be designed, because the old arc lighting was a product 
of the silent picture days, before the recording of sound. 

The studios that purchased the modern arc equipment for color purposes very 
rapidly began to use it in their black-and-white sets. Many cameramen, all 
through the transition from silent to sound and from orthochromatic through the 
various stages of panchromatic film emulsions, had always used a considerable 
amount of arc lighting. There was something they felt they could obtain in the 
definition and quality of the picture by utilizing arc illumination. 

Film speeds are now becoming very high, and for a while we see trends swinging 
away from arc lighting toward Mazda, and then again the trends reverse. That is 
due sometimes to styles of photographic taste, because they also change. When 
one of the cameramen does a job that is recognized as a fine piece of camera work, 
other cameramen try to gather which way the wind is blowing and try to follow 
the trend of the public's and the critic's desire. 



NEW MOTION PICTURE APPARATUS 

During the Conventions of the Society, symposiums on new motion picture appara- 
tus are held in which various manufacturers of equipment describe and demonstrate 
their new products and developments. Some of this equipment is described in the 
following pages; the remainder will be published in subsequent issues of the Journal. 

NEW LENSES FOR PROJECTING MOTION PICTURES* 

W. B. RAYTON** 



Since the early days of the industry, motion picture exhibitors have usually 
been searching for increased illumination. Among the reasons that at various 
times have led to this demand have been a desire for larger picture sizes, the 
introduction of perforated screens with a consequent reduction in reflectivity, 
the use of low key-lighting in the studios, and the growing use of color. The 
equipment manufacturers have constantly striven to satisfy the needs of the pro- 
jectionist and the history of their activities consists of a constant series of im- 
provements in sources of light, lamp houses, the optics of the illuminating system, 
and in projection lenses. This brief paper is offered to put on record two new 
series of projection lenses which constitute another step in this long record of 
advancements in equipment design. 

Both series are made with a relative aperture of //2.O. It is to be understood 
that no claim is made that this is the first time that projection lenses with a 
relative aperture of this size have been made. In fact, lenses of considerably 
higher apertures have been made, although to what purpose it is difficult to see, 
if considered for theater projection with an arc lamp as the source of light. 

The first series is called the Super Cinephor //2.O. It is available in focal 
lengths from 2 to 5 inches for use in theater practice. Focal lengths of 6, 7, and 8 
inches are also available but can not be used on existing projectors because of the 
limitations of the lens holder. They are made primarily for use in background 
projection in motion picture studios. These lenses are anastigmats, which is to 
say, they are simultaneously corrected for astigmatism and curvature of field. 
Speaking before this Society in April, 1927, 1 and commenting on a tendency that 
seemed to be developing at that time of building theaters with short projection 
distances and large screens, I made the statement that this tendency seemed likely 
to compel the use of anastigmat constructions in motion picture projection, but 
that if this result followed, it would be possible only by reducing the relative 

* Presented at the 1940 Spring Meeting at Atlantic City, N. J.; received April 
29, 1940. 

** Bausch & Lomb Optical Co., Rochester, N. Y. 



90 



NEW MOTION PICTURE APPARATUS [J. S. M. P. E. 



aperture of the projection lens or accepting a lower quality of definition over the 
whole picture area. In spite of this somewhat pessimistic view, in three years we 
had designed and made available an anastigmat with a relative aperture of f/2.3 
which was faster than the majority of projection lenses then in use, whose central 
definition was at least equal to anything in use at the time, and with greatly 
superior definition at the margin of the field. This was the//2.3 Super Cinephor, 
undoubtedly the finest lens that had ever been offered up to that time for the 
projection of motion pictures. Because of its complex construction and the 
dense barium crown glass used therein, the light transmission was considerably 
less than that of lenses of the Petzval type commonly in use. In spite of this 
handicap, acceptance of the lens exceeded our expectations. Nevertheless, we 
did not feel satisfied to let the matter rest at that point, but continued with ex- 
periments looking toward a new design with still greater relative aperture and 




FIG. 1. Super Cinephor 5-inch, //2.O. 

employing glass of higher transparency. The result is a lens of the type shown 
in Fig. 1, in which the crown elements are made of light barium crown glass of 
high transparency and in which the corrections have been perfected for a relative 
aperture off/2.0 to such a point that an image of unimpeachable quality over the 
whole area of the screen is produced. 

At just about the time we were ready to announce these lenses, experiments 
which had been going on in various parts of the country on anti-reflection treat- 
ment of glass surfaces 2 - 3 - 4 had reached a point where it seemed practicable to in- 
corporate such a feature in the lens in question and thereby obtain a very sub- 
stantial increase in its light transmission and, consequently, in the brightness of 
the projected image. Release of the lenses was therefore held up in order to per- 
mit the surface treatment to be incorporated. Experiments were conducted in 
motion picture theaters in order to satisfy ourselves reasonably well as to the 
durability of the surfaces in service. These experiments seemed to indicate that 
there was no reason to question their permanence except that the results of the 
usual method of treatment will not stand the cleaning process as ordinarily em- 



July, 1940] 



NEW MOTION PICTURE APPARATUS 



91 



ployed on lens surfaces. In order to overcome the possible difficulty offered by 
this condition, we have gone a step farther and have sealed the lenses air-tight 
so that they neither need to be taken apart for cleaning nor can they be taken 
apart except at the factory. This leaves all surfaces completely protected against 
dust, moisture, and oil vapor, except the outside surfaces. The treatment applied 
to the outside surfaces is, however, such as to make it possible to clean them in 
the ordinary manner. Fortunately, the glass employed in the construction is one 
of the few that permits an effective treatment in this way. 

The question naturally arises as to how much increase in illumination may be 
expected from these lenses. It is impossible to answer this question in such a way 
that it has a definite meaning for any particular installation. We can make some 
assumptions, however, and on the basis of those assumptions state what may be 
expected. If we assume that the basis of comparison is a lens of relative aperture 





FIG. 2. Cinephor 5-inch, //2.O. 



of //2.4, a lens of the same type with a relative aperture of //2.0 will transmit 44 
per cent more light, assuming that the aperture is completely filled by the illumi- 
nant. The effect of surface treatment is to provide a further increase of illumina- 
tion of from 25 to 30 per cent. 

Because of the fact that it has 8 air-glass surfaces as against 6 in the ordinary 
Petzval type of projection lens, the light transmission of the//2.0 Super Cinephor 
will be about 88 per cent of the transmission of the Petzval type of lens such as, for 
example, the Bausch & Lomb Cinephor lens. If we assume 27 per cent as the 
average gain in transmission due to surface treatment, then, combining all factors, 
the treated //2.0 Super Cinephor should show a gain of 61 per cent over an//2.4 
untreated lens of the Petzval construction. 

This can be realized only if the illuminant is competent to utilize all of the 
aperture of the lens. Such illuminants do not exist. Some of the high-intensity re- 
flector arcs, however, are competent to utilize a relative aperture of 2.2. As com- 
pared to an //2.4, this represents a gain due to aperture of 19 per cent. Com- 



92 NEW MOTION PICTURE APPARATUS [J. S. M. P. E. 

bining this with the gain due to surface treatment and the 12 per cent loss due to 
increased number of air-glass surfaces, the resulting possible increase is still 33 
per cent with reference to a Cinephor lens of a speed of //2.4, and at the same time 
this is accomplished with a flatter field of view. 

As to whether //2.0 illuminants are practical, it is not the purpose of this paper 
to deal. A report was presented to this Society at the 1939 Fall Meeting covering 
some experiments that had been made in this direction. 6 

In addition to the increase of brightness of the projected image, experience has 
shown that the surface treatment has a further beneficial effect in the reduction 
of veiling glare and increasing the contrast of the image. Projectionists who were 
given experimental lenses for trial unanimously and voluntarily reported in- 
creased contrast and apparently improved sharpness of definition. The latter 
can not result from any actual reduction of aberrations, but must be the effect 
of improved contrast. It is well known that any stray light on the screen will 
result in a loss of contrast. In untreated surfaces, light is reflected from each air- 
glass surface back toward the light-source. Some of this light is again reflected 
by other surfaces toward the screen. Another fraction of the light reflected back 
toward the source falls upon the film and by it is again reflected forward and 
reaches the screen. Both of these result in a certain amount of light appearing 
in areas that should be black. Reducing the amount of reflection has a very de- 
cided effect in improving the general appearance of the projected image. 

We believe the lens just described represents the highest point yet achieved in 
projection lens performance. It combines all the advancements in the art so far 
developed. Longer focal lengths could be supplied if projection machines were 
provided with lens holders competent to receive them. Until such changes are 
made in projectors, however, it is impossible to employ in theater projection 
lenses with a speed of //2.0 in focal lengths longer than 5 inches. The lens is 
made in focal lengths from 2 to 5 inches in 1 /4-inch steps. 

At the same time, a second series of lenses has been designed with a speed of 
//2.0 of the Petzval type, shown in Fig. 2. In order to maintain good definition 
with the increased relative aperture it has been necessary to increase the length 
as compared to the old Cinephor and this leads to a decreased back focus. At the 
same time it is necessary to maintain such a diameter for the back components as 
to make it impossible to adapt these lenses to projectors of designs prior to cur- 
rent manufacturing models. This lens was designed to give high speed at the 
lowest possible price. It is offered, therefore, without the special features that 
characterize the Super Cinephor: namely, treatment of surfaces and sealing, fea- 
tures that can be added only at a substantial increase in price. The same condi- 
tion that limits the focal length of the //2.0 Super Cinephor to 5 inches applies 
also to this case, so that there is no point in making these lenses in focal lengths 
longer than 5 inches. They are offered in a series beginning with 3 inches and 
extending to 5 inches, in 1 /4-inch steps. 

REFERENCES 

1 RAYTON, W. B.: "Some Facts Concerning Projection Lenses," Trans. Soc. 
Mot. Pict. Eng., XI (April, 1927), No. 29, p. 101. 

8 STRONG, J.: "On a Method of Decreasing the Reflection from Nonmetallic 
Substances," /. Opt. Soc. Amer., XXVI (Jan., 1936), No. 1, p. 73. 



July, 1940] NEW MOTION PICTURE APPARATUS 93 

1 CARTWRIGHT, C. H. : "Treatment of Camera Lenses with Low-Reflecting 
Films," J. Opt. Soc. Amer., XXX (Mar., 1940), No. 3, p. 110. 

4 SxuLL, W.: "Non-Glare Coating Makes Lenses One Stop Faster," Amer. 
Cinemat., XXI (Mar., 1940), p. 108. 

8 JOY, D. B., LOZIER, W. W., AND SIMON, R. W.: "Large-Size Non-Rotating 
High-Intensity Carbons and Their Application to Motion Picture Projection," 
/. Soc. Mot. Pict. Eng., XXXTV (Mar., 1940), p. 241. 

DISCUSSION 

MR. RICHARDSON: How long do you think the sealed interior surfaces will 
require no attention? 

DR. RAYTON: I can only hazard a guess, based on our experience of one year 
with such lenses in theater practice, in daily use. These lenses showed no signs of 
change of the internal surfaces within that length of time. I dare say that the 
answer to the question depends entirely upon the durability of the seal, and I 
suppose in the course of time that material may break down and permit the lens 
to begin to pump air. It seems to me that it is safe to hazard a guess that that 
will not happen in less than five years maybe ten years. 

MR. KELLOGG: What is the magnitude of absorption in the glass? 

DR. RAYTON: In optical glass it is half a per cent per cm, and from that on up 
to 2 per cent in glasses still usable in optical instruments. In other kinds of glass 
window glass and the like, it can, of course, reach very much higher figures. 

MR. RICHARDSON: Mr. W. C. Miller tells me that in lenses treated for camera 
work an unexpected phenomenon was found. In photography there appears to 
be an advantage beyond the apparent improvement in transmission. Untreated 
lenses producing flare apparently put an overall fog upon the emulsion of the film, 
upon which the photographic image has to be superimposed, and apparently the 
film must be unduly exposed to superimpose the image upon the fog so produced. 
Is that explanation valid? I am interested to see whether or not in projection we 
have been having a similar situation on the screen. 

DR. RAYTON: Both in projection and in photography, I think the answer is 
yes. With a projected image of good contrast, a better subjective reaction is 
obtained with a lower level of illumination than with a higher level of illumination, 
if the contrast is poor. I have seen examples of photography done with these 
lenses that seem to prove Mr. Miller's point, although it is not a factor that can be 
expressed quantitatively. Personally, I am leaving it out of consideration in any 
quantitative statements in connection with projection. It is a factor of real sig- 
nificance, but I do not know how it can be measured quantitatively. 

MR. FARNHAM: I believe that the average surface loss is 4 to 5 per cent. To 
what value does this treatment bring it? 

DR. RAYTON: Actual surface loss may run to higher than 5 per cent. It 
depends upon the index of reflection of the glass; 5.5 per cent is sometimes given. 
Some lenses average 5.5 per cent loss per surface. The reduction of reflected 
light, by evaporating films on the surface can reach, I should say, a figure of three- 
quarters of the originally reflected factor. Perhaps it is not too much to assume 
that it can be reduced to 1 per cent per surface. That is perhaps a little opti- 
mistic, but for convenience and calculation it is fair enough. 



94 NEW MOTION PICTURE APPARATUS [J. S. M. P. E. 

There is a tendency in some of the literature to be a bit over-optimistic with 
respect of the gain in transmission. Please bear in mind that it would be utterly 
impossible to gain something under the circumstances that is not taken away in 
the first place. If we have a lens system whose maximum loss, due to reflection, 
is 30 per cent, it is absurd to say that the transmission of the lens can be increased 
50 per cent by any surface treatment, because we should have to reduce the light 
lost by reflection by more than 100 per cent. 

MR. C. TUTTLE:* In a paper which Dr. Jones and I published in the TRANS- 
ACTIONS of this Society in 1926, we discussed the magnitude of the screen image 
contrast reduction resulting from projection lens flare. The total amount of this 
effect is dependent in a marked degree upon the overall density of the picture 
the more transparent the frame, the greater the contrast reduction. Though the 
effect occurs in the most noticeable degree in the shadow region of the picture, it 
also influences the whole tone reproduction curve in a manner somewhat similar 
to that produced by a reduction of positive gradient by lowered release print de- 
velopment. The data which we then presented, coupled with data on average 
release print densities which I presented in the JOURNAL in May, 1936, led to the 
conclusion that, on the average, a flareless lens system might be expected to 
yield a screen image in which the gradient of the reproduction curve would be 
from 15 to 20 per cent higher than that of a system with the usual amount of 
flare. 

This point, by itself, is worthy of consideration by the release-print labora- 
tories, since it is obvious that if a given print is to be projected through one of 
these treated lenses in one case, and through an untreated lens in another case, 
the variation in contrast resulting from the single uncertainty would be as great 
as or greater than the contrast variation from print to print, according to the 
development-tolerance standards now in effect in the release-print laboratories. 

Another and probably more important aspect of the effect of lens treatment is 
its possible influence upon the Society's recommendations of screen brightness. 

In 1936 the Screen Brightness Committee recommended 7 to 14 foot-lamberts. 
This recommendation was later accepted by the Standards Committee and 
adopted into the "Recommended Practice" sections of the Society standards. 

The value of 7 foot-lamberts was considered as possibly too low for a low limit, 
but it was selected by the Committee because it was the highest value which 
could be obtained with the best of the then-existing equipment on large screens, 
e. ., 30 feet wide. 

Now Mr. Rayton gives us hope of a 30 per cent increase in efficiency of putting 
light on the screen. I call to the attention of the Standards Committee that the 
reason for the value 7 no longer exists; perhaps it should be changed to 9. 

The Screen Brightness Committee fixed on the upper value of 14 on the basis 
of what it considered to be an allowable variation of the apparent quality of the 
picture as a function of the brightness change. This matter is discussed in the 
committee report published in August, 1936. 

The contrast-seeing ability increases with brightness this change being ap- 
proximately 15 per cent for a doubling of brightness. Thus, as treated lenses 
come into use, two distinct effects tend to increase the screen-image contrast 

* Communicated. 



July, 1940] NEW MOTION PICTURE APPARATUS 95 

the first resulting from a decrease of flare, the second from the increase of bright- 
ness. 

It appears to me that if, as argued by the Screen Brightness Committee, the 
allowable variation in apparent image contrast is to fix the screen brightness 
tolerance, then it follows that the introduction of treated projection lenses should 
decrease the screen brightness tolerance. For some time both treated and un- 
treated lenses will be in general use, and it is probably not a good idea to recom- 
mend new practice standards of 9 to 18 foot-lamberts because if release-print 
contrast is adjusted to look right at 9 foot-lamberts with an untreated lens, a 
given print will then have too high contrast if projected at 18 foot-lamberts with 
an untreated lens. 

At a guess, a reasonable recommendation to fit present conditions would be 
9 to 14 or 15 foot-lamberts. 

MR. WELMAN: The earlier //2.3 Super Cinephor was not a Petzval lens, was 
it? 

DR. RAYTON: No. 

MR. WELMAN: You made your comparison of 30 per cent by comparing the 
new lens with the Petzval //2. 4. What would be the comparison of this lens with 
the earlier Super Cinephor of 2.3? 

DR. RAYTON: The product of the three factors that I mentioned as contrib- 
uting to increased illumination at the maximum brought us to a value of 61 per 
cent, comparing the new Super Cinephor against the old //2.4 Cinephor. Com- 
pared with the old Super Cinephor you would add another 10 or 12 per cent. 

MR. MAURER: A great deal of what Dr. Rayton has told us is of decided in- 
terest in the 16-mm field. The comment has often been made to me by competent 
observers that the quality of the lenses in general use for 16-mm projections leaves 
a great deal to be desired. It is generally, and I think somewhat erroneously, 
assumed that 16-mm equipment must be held down to low cost in all its compon- 
ents. As a result, sometimes we find what I feel to have been unnecessary and 
undesirable sacrifices of quality in overall results. 

With that in mind, I should like to ask Dr. Rayton, not with a view to accuracy, 
but just as to the general order of magnitude, what are the comparative costs of 
the Anastigmat Super Cinephor construction and the Petzval type of construction 
commonly used for 16-mm projection lenses? 

DR. RAYTON : Between perhaps 5 and 10. 

MR. KELLOGG : If you look back toward the projector in a theater, you see an 
impressive amount of light coming from the lens surface, and also from the light- 
beam, due to scattering by the dust in the air, or smoke. I wonder whether the 
light scattered in this manner is much of a factor in making haze on the screen. 
Also, how much of the light scattered by the lens surface may be due to dust and 
scratches? These specks look intensely brilliant when you look at the lens from 
close by. 

DR. RAYTON: There is no doubt that dust on lens surfaces is responsible for 
considerable diffusely distributed light. It is not so bad that every last speck of 
dust has to be removed, or that one should worry about every little scratch that 
appears on a lens surface. Nevertheless, many lenses are used in a condition that 
is practically criminal, from the standpoint of the quality of the image. 

MR. ROBERTS: What is the relative efficacy of the two treatments used in the 



96 NEW MOTION PICTURE APPARATUS [J. S. M. P. E. 

Super Cinephor; or, what is the difference between the coating used for the inside 
surfaces, which I understand is a relatively perishable coating, and the external 
treatment which can be handled a little bit more roughly? 

DR. RAYTON: We can only answer the question for the particular kind of glass 
employed in this construction. Whereas the applied coating can produce an 
effect equivalent to reducing reflection to one-quarter of its original value, the 
other method used on the external surfaces reduces it to one-half its original value. 
The difference between the two methods, if applied to the external surfaces, will 
affect the transmission of the lens perhaps 5 per cent. 

MR. ROBERTS: Can the outside treatment be applied to eye-glasses? 

DR. RAYTON: It can not be employed on the glass ordinarily used on eye- 
glasses. 

MR. HOVER: I suspect there will be many projectionists who will worry about 
the sealing of the lens. We might remember that some of us have the better 
grade of optical systems in the sound mechanisms and those lenses are sealed. 
I have one pair, of excellent make, that has worked a little over five years, without 
any difficulties whatever, and I believe that the optical system in the sound 
mechanism frequently (the rear of it, at least) operates at a rather high tempera- 
ture. 

MR. KURLANDER: What is the absolute transmission constant of the Super 
Cinephor lens having eight air-glass surfaces, treated and untreated? 

DR. RAYTON: Approximately 65 per cent for the untreated lens, and from 80 
to 85 per cent for the treated lens. 

MR. FRANK: The //2 Super Cinephor lens can be used only in the current 
models of projectors, such as the Simplex, the Super Simplex, and the E-7. By 
modifying the lens holders of the older models, which the manufacturers are pre- 
pared to do at a reasonable cost, these lenses can be used with them. I am a little 
uncertain, however, concerning the statement you made as to whether the same 
thing is true in the case of the//2 Cinephor lens, or whether I am to interpret your 
statement as meaning that under no conditions can the//2 Cinephor be used with 
the older model of the Simplex projector. 

It should be pointed out also that the old Series 2 Cinephor lenses are available 
only with treated surfaces, and the less expensive type, as heretofore, without 
treated surfaces, is no longer manufactured. 

MR. SCHEICK: Any of our lenses can be supported without any unusual adapt- 
ors in the Super Simplex and the E-7 Simplex. But in the old standard Simplex 
mechanism it will be necessary to use the special adaptor you have built called the 
62-C, which will support any of the lenses whatsoever in that mechanism. 

MR. KURLANDER: What is the method of sealing employed? 

DR. RAYTON: It is the same type of sealing that has been used successfully in 
the sound reproducer the use of a gasket and a material that is oil-proof and 
maintains its elasticity indefinitely. 

MR. PALMER : One point discussed at the Atlantic Coast Section Meeting, at 
which the coated lenses were demonstrated, was whether there is a color difference 
in the light projected through coated and uncoated lenses. 

DR. RAYTON: Undoubtedly there is a difference, just as there is a color differ- 
ence in the light reflected from ordinary glass surfaces. The question is probably 
inspired largely by the fact that the appearance of these treated surfaces is de- 



July, 1940] NEW MOTION PICTURE APPARATUS 97 

cidedly colored. However, when you stop to think that the amount of light re- 
flected from them only amounts to, say, 1 per cent of the incident light, any selec- 
tivity in that 1 per cent ceases to have much significance. If there is selectivity in 
the 1 per cent, there is the same selectivity, or the complement of it, in the trans- 
mitted light. Undoubtedly, if sufficiently precise measurements had been made 
spectrophotometrically, there is a change in the color of the transmitted light. 
That can be controlled to a considerable extent in the applied process. That is 
one of the factors that has to be watched in the practical application of the treat- 
ment, and careful attention is given to it. I do not think that, controlled in that 
way, the results can create any color disturbance of any significance. 



CURRENT LITERATURE OF INTEREST TO THE MOTION PICTURE 

ENGINEER 



The editors present for convenient reference a list of articles dealing with subjects 
cognate to motion picture engineering published in a number of selected journals. 
Photostatic copies may be obtained from the Library of Congress, Washington, D. C., 
or from the New York Public Library, New York, N. Y. Micro copies of articles 
in magazines that are available may be obtained from the Bibliofilm Service, Depart- 
ment of Agriculture, Washington, D. C. 

Bell Laboratories Record 

18 (May, 1940), No. 9 
Stereophonic Reproduction from Film (pp. 260-265) HARVEY FLETCHER 

British Journal of Photography 

87 (April 19, 1940), No. 4172 
Progress in Colour (pp. 192-194) 

Educational Screen 

19 (May, 1940), No. 5 
Motion Pictures Not for Theaters (pp. 193-197) A. E. KROWS 

Electronics 

13 (May, 1940), No. 5 
Photoelectric Tape Recording (pp. 16-18) 
Enhanced Stereophonic Recordings Demonstrated by 
Bell Laboratories (pp. 30-31) 

13 (June, 1940), No. 6 
Television Receivers Using Electrostatic Deflection 

(pp. 16-19, 89) T. T. GOLDSMITH, JR. 

Electronics and Television and Short-Wave World 

13 (May, 1940), No. 147 
Improved Materials for Fluorescent Screens (p. 236) 

Institute of Radio Engineers, Proc. 

28 (April, 1940), No. 4 
The Gradation of Television Pictures (pp. 170-174) H. E. KALLMANN 

International Projectionist 

15 (April, 1940), No. 4 

Stereophonic Reproduction from Film (pp. 14, 17-18) H. FLETCHER 
The Influence of Sound Accompaniment on the Dra- 
matic Value of Pictures (pp. 20-21) 



CURRENT LITERATURE 99 

Regeneration and Preservation of Film (p. 22) A. KALIX 

15 (May, 1940), No. 5 
Fundamentals of Theater Acoustics (pp. 7-8, 11) J. E. VOLKMANN AND 

K. C. MORRICAL 
Pro and Con Views of the Switzer Electronic Carbon 

Arc Control (pp. 12, 15, 16-17) F. L. HILL AND G. 

SWITZER 

Optical Society of America, Journal 

30 (May, 1940), No. 5 
The Carbon Arc as a Radiation Standard (pp. 189-194) H. G. MACPHERSON 



1940 FALL CONVENTION 
SOCIETY OF MOTION PICTURE ENGINEERS 



HOLLYWOOD ROOSEVELT HOTEL 

HOLLYWOOD, CALIFORNIA 
OCTOBER 21st-25th, INCLUSIVE 



Officers and Committees in Charge 

E. A. WILLIFORD, President 

N. LEVINSON, Executive Vice-P resident 

W. C. KUNZMANN, Convention Vice-President 

J. I. CRABTREE, Editorial Vice-P resident 

L. L. RYDER, Chairman, Pacific Coast Section 

H. G. TASKER, Chairman, Local Arrangements Committee 



Pacific Coast Papers Committee 

O. O. CECCARINI C. N. BATSEL F. M. FALGE 

G. CHAMBERS W. A. MUELLER C. R. SAWYER 

L. D. GRIGNON H. G. TASKER R. TOWNSEND 



Reception and Local Arrangements 

H. G. TASKER, Chairman 

N. LEVINSON G. F. RACKETT E. HUSE 

K. F. MORGAN H. W. MOYSE J. O. AALBERG 

P. MOLE W. C. MILLER R. H. McCuLLOUGH 

A. M. GUNDELFINGER W. A. MUELLER J. M. NlCKOLAUS 

H. W. REMERSCHIED C. L. LOOTENS E. H. HANSEN 

G. S. MITCHELL W. V. WOLFE R. G. LINDERMAN 

L. D. GRIGNON E. C. RICHARDSON F. M. FALGE 



Registration and Information 

W. C. KUNZMANN, Chairman 
C. W. HANDLEY J. FRANK, JR. 

S. HARRIS W. R. GREENE 

100 



H. T. KALMUS 
E. HUSE 
L. L. RYDER 
C. DUNNING 

R. G. LlNDERMAN 



FALL CONVENTION 
Banquet and Dance 

N. LEVINSON, Chairman 
G. S. MITCHELL 
P. MOLE 
H. G. TASKER 
W. C. MILLER 

R. H. McCULLOUGH 



101 



G. F. RACKETT 
J. O. AALBERG 
K. F. MORGAN 
H. W. MOYSE 

J. L. COURCIER 



Hotel and Transportation 



W. C. HARCUS 
F. L. EICH 
E. M. HONAN 
H. R. LUBCKE 
W. E. THEISEN 



G. A. CHAMBERS, Chairman 

L. M. HOFFMAN 

S. P. SOLOW 

D. P. LOYE 

D. J. BLOOMBERG 

F. J. DURST 



K. B. LAMBERT 

F. O'GRADY 

A. C. BLANEY 
D. B. BROWN 
J. G. FRAYNE 



J. O. AALBERG 
C. W. HANDLEY 
W. F. RUDOLPH 
J. M. NICKOLAUS 

J. K. HlLLIARD 



Convention Projection 

H. GRIFFIN, Chairman 
H. A. STARKE 
L. E. CLARK 
M. S. LESHING 
A. F. EDOUART 
I. SERRURIER 



J. DURST 

R. H. McCULLOUGH 

H. W. REMERSCHIED 
H. I. REISKIND 
W. W. LINDSAY, JR. 



Officers and Members of Los Angeles Projectionists Local No. 150 



Ladies' Reception Committee 



MRS. L. L. RYDER, Hostess 
assisted by 



MRS. H. G. TASKER MRS. N. LEVINSON 
MRS. E. C. RICHARDSON MRS. P. MOLE 
MRS. G. F. RACKETT 
MRS. H. W. MOYSE 
MRS. L. E. CLARK 
MRS. G. S. MITCHELL 



MRS. C. W. HANDLEY 
MRS. K. F. MORGAN 
MRS. W. C. MILLER 
MRS. B. KREUZER 



MRS. E. HUSB 
MRS. G. A. CHAMBERS 
MRS. J. O. AALBERG 
MRS. R. H. MCCULLOUGH 
MRS. C. DUNNING 
MRS. F. J. DURST 



MRS. A. M. GUNDELFINGER 



Miss Ruth Williams, Social Director, Hollywood Roosevelt Hotel 



L. A. AICHOLTZ 
W. A. MUELLER 



Publicity 

J. HABER, Chairman 
W. R. GREENE 
G. CHAMBERS 



S. HARRIS 

A. M. GUNDELFINGER 



102 FALL CONVENTION [J. S. M. P. E. 

New Equipment Exhibit 

B. KREUZER, Chairman 

P. MOLE F. J. DURST J. G. FRAYNE 

C. N. BATSEL O. F. NEU H. W. REMERSCHIED 

K. F. MORGAN F. M. FALGE C. R. DAILY 

P. F. HARPER G. H. WORRALL C. W. HANDLEY 

Headquarters 

Headquarters of the Convention will be the Hollywood Roosevelt Hotel, where 
excellent accommodations are assured. A reception suite will be provided for the 
Ladies' Committee, and an excellent program of entertainment will be arranged 
for the ladies who attend the Convention. 

Daily hotel rates to SMPE delegates will be as follows (European Plan) : 

One person, room and bath $ 3 . 50 

Two persons, double bed and bath 5.00 

Two persons, twin beds and bath 6 . 00 

Parlor suite and bath, 1 person 8.00-14.00 

Parlor suite and bath, 2 persons 12 . 00-16 . 00 

Room reservation cards will be mailed to the membership early in September, 
and should be returned to the Hotel immediately to be assured of satisfactory 
accommodations. 

Indoor and outdoor garage facilities adjacent to the Hotel will be available to 
those who motor to the Convention. 

Members and guests of the Society will be expected to register immediately upon 
arriving at the Hotel. Convention badges and identification cards will be sup- 
plied which will be required for admittance to the various sessions, studios, and 
several Hollywood motion picture theaters. 

Railroad Fares 

The following table lists the railroad fares and Pullman charges: 

Railroad Fare Pullman 

City (round trip) (one way) 

Washington $132.20 $22.35 

Chicago 90.30 16.55 

Boston 135.00 23.65 

Detroit 106.75 19.20 

New York 135.00 22.85 

Rochester 124.05 20.50 

Cleveland 111.00 19.20 

Philadelphia 135.00 22.35 

Pittsburgh 117.40 19.70 

The railroad fares given above are for round trips. Arrangements may be 
made with the railroads to take different routes going and coming, if so desired, 



July, 1940 J FALL CONVENTION 103 

but once the choice is made it must be adhered to, as changes in the itinerary may 
be effected only with considerable difficulty and formality. Delegates should 
consult their local passenger agents as to schedules, rates, and stop-over privileges. 

Technical Sessions 

The Hollywood meeting always offers our membership an opportunity to be- 
come better acquainted with the studio technicians and production problems. 
Technical sessions will be held in the Blossom Room of the Hotel. Several eve- 
ning meetings will be arranged to permit attendance and participation by those 
whose work will not permit them to be free at other times. The Local Papers 
Committee is collaborating closely with the General Papers Committee in arrang- 
ing the details of the program. 

Studio Visits 

The Local Arrangements Committee is planning visits to several studios during 
the Convention week. Details will be announced in the next issue of the JOURNAL. 
Admittance to the studios will be by registration card or Convention badge only. 

New Equipment Exhibit 

An exhibit of newly developed motion picture equipment will be held in the 
Bombay and Singapore Rooms of the Hotel, on the mezzanine. Those who wish 
to enter their equipment in this exhibit should communicate as early as possible 
with the General Office of the Society at the Hotel Pennsylvania, New York, N. Y. 

Semi- Annual Banquet and Dance 

The Semi-Annual Banquet of the Society will be held at the Hotel on Wednes- 
day, October 23rd, in the Blossom Room. A feature of the evening will be the 
annual presentations of the SMPE Progress Medal and the SMPE Journal Award. 
Officers-elect for 1941 will be announced and introduced, and brief addresses will 
be delivered by prominent members of the motion picture industry. The eve- 
ning will conclude with entertainment and dancing. 

The Informal Get-Together Luncheon will be held in the Florentine Room of 
the Hotel on Monday, October 21st, at 12:30 p. M. 

Motion Pictures 

At the time of registering, passes will be issued to the delegates to the Conven- 
tion, admitting them to the following motion picture theaters in Hollywood, by 
courtesy of the companies named: Grauman's Chinese and Egyptian Theaters 
(Fox West Coast Theaters Corp.), Warner's Hollywood Theater (Warner Brothers 
Theaters, Inc.), Pantages Hollywood Theater (Rodney Pantages, Inc.). These 
passes will be valid for the duration of the Convention. 

Ladies' Program 

An especially attractive program for the ladies attending the Convention is 
being arranged by Mrs. L. L. Ryder, hostess, and the Ladies' Committee. A suite 



104 FALL CONVENTION 

will be provided in the Hotel, where the ladies will register and meet for the 
various events upon their program. Further details will be published in a suc- 
ceeding issue of the JOURNAL. 

Points of Interest 

En route: Boulder Dam, Las Vegas, Nevada; and the various National Parks. 

Hollywood and vicinity: Beautiful Catalina Island; Zeiss Planetarium; Mt. 
Wilson Observatory ; Lookout Point, on Lookout Mountain ; Huntington Library 
and Art Gallery (by appointment only) ; Palm Springs, Calif. ; Beaches at Ocean 
Park and Venice, Calif.; famous old Spanish missions; Los Angeles Museum 
(housing the SMPE motion picture exhibit); Mexican village and street, Los 
Angeles. 

In addition, numerous interesting side trips may be made to various points 
throughout the West, both by railroad and bus. Among the bus trips available 
are those to Santa Barbara, Death Valley, Agua Caliente, Laguna, Pasadena, and 
Palm Springs, and special tours may be made throughout the Hollywood area, 
visiting the motion picture and radio studios. 

W. C. KUNZMANN, 

Convention Vice-President 



SOCIETY ANNOUNCEMENTS 



1940 FALL CONVENTION AT HOLLYWOOD 

The next Convention of the Society will be held at the Hollywood Roosevelt 
Hotel, Hollywood, Calif., October 21st-25th, inclusive. Details of the Convention 
are presented in a preceding section of this issue of the JOURNAL, and further in- 
formation regarding the papers program will be published in succeeding issues. 

All persons wishing to present papers at the meeting should communicate im- 
mediately with the General Office of the Society at the Hotel Pennsylvania, New 
York, N. Y. 

PACIFIC COAST SECTION 

At a meeting held on June 17th at the Paramount Studio Theater in Holly- 
wood, Calif., Mr. W. C. Miller of the Vard Mechanical Laboratories, Pasadena, 
Calif., discussed the treatment of lenses for decreasing the reflection of light from 
the lens surfaces. This was a re-presentation of Mr. Miller's paper originally pre- 
sented at the Atlantic City Convention of the Society in April, entitled "Speed Up 
Your Lens Systems." 

"The Application of Lens Surface Treatments to Sound Optical Systems," 
was discussed by Dr. J. G. Frayne of Electrical Research Products, Inc., and C. M. 
Batsel of the RCA Manufacturing Company. 

The meeting was concluded by showing of a picture produced by Messrs. R. B. 
Atkinson and S. P. Solow entitled "The Alchemist hi Hollywood." 



THE EXPANDED PROGRAM 
OF THE 

RESEARCH COUNCIL OF THE ACADEMY OF MOTION PICTURE 
ARTS AND SCIENCES* 

DARRYL F. ZANUCK** 

Due to the success of the past efforts of the Research Council of the Academy 
of Motion Picture Arts and Sciences, the Council is appointing new Basic Com- 
mittees in the fields of photography, sound, optics, laboratory, and cine-technical 

* Extract from address at a general conference held at Hollywood May 29, 
1940, for the inauguration of the Research Council's new Basic Committee 
organization. 

** Chairman of the Research Council. 

105 



106 SOCIETY ANNOUNCEMENTS [J. S. M. P. E. 

development. These new Committees will multiply the past benefits resulting 
from the Council's activities and will return the utmost value to the industry 
from these efforts. 

Before going into the details of the operation of these new Basic Committees, 
a short historical background of the Research Council may be of interest. The 
Academy of Motion Picture Arts and Sciences was originally organized in 1927, 
for the principal purposes of advancing the arts and sciences of motion pictures 
and fostering cooperation among the leadership of the motion picture industry 
for cultural, educational, and technical progress. 

Within the Academy the motion picture industry has set up its Research 
Council, the entire purpose of which is the "scientific advancement of the motion 
picture industry through cooperative research, investigation, and development of 
equipment, practices, technics. Also the promotion of the interchange of ideas 
and information as pertaining to the motion picture industry; the furtherance 
of professional and vocational education of motion picture technicians; and the 
dissemination of information throughout the world by means of conferences, 
meetings, and publications." 

The Academy Research Council is concerned with projects involving investi- 
gation beyond the facilities of any individual studio and which can be handled 
more efficiently and more economically by cooperative effort. 

The Academy Research Council is responsible for all matters of standardiza- 
tion on behalf of the motion picture studios, cooperating with the various equip- 
ment manufacturers and supply companies and coordinating its activities with 
the standardization activities of the Society of Motion Picture Engineers, and 
the Sectional Committee on Motion Pictures of the American Standards Associa- 
tion. 

The newly appointed Basic Committees will direct the cooperative conduct 
of all projects in their respective fields. Each of the Committees consists in 
general of a representative from each of the studios sponsoring the Council, 
thus giving each producing company the benefit of the efforts of the best tech- 
nical personnel in the industry. 

The responsibility for the policies and the general direction of the whole co- 
operative program is in the hands of the Research Council, the membership of 
which also consists of one representative from each of our sponsoring companies. 
It is intended that the Chairman of each of the Basic Committees shall serve as 
ex-officio members of the Council and will thus assist in its deliberations. 

Each Basic Committee will appoint as many Subcommittees as may be neces- 
sary to conduct the various projects in each field, and will be responsible for the 
coordination of the work of all these Subcommittees. 

All Basic Committees will immediately survey their entire field and inaugurate 
such investigations which the Council, in consultation with the Committee 
Chairmen, may deem advisable. Many problems brought to the Council's 
attention since the original announcement of the expanded activities will also be 
transmitted to the proper Basic Committees. 

Facilities of all the studios are of course available to the Council and its Com- 
mittees. As in the past, it is anticipated that the equipment companies will 
actively cooperate in the work, continuing to offer and give of their time and 
facilities as needed to further the Research Council program. 



July, 1940] 



SOCIETY ANNOUNCEMENTS 



107 



The expanded Research Council will provide a smoothly operating and ef- 
ficiently functioning organization, capable of immediately handling all problems 
coming within its scope. The entire plan of operation is founded upon the 
recognition of the value of careful judgment based upon an orderly study of all 
the facts. 

In practice the following procedure will be followed : A new project or an exist- 
ing problem may be brought to the attention of the Research Council by anyone 
connected with the motion picture industry. The problem will then be given 
consideration by the Council, to decide to which one, if any, of the Basic Com- 
mittees it will be referred. The Basic Committee will then lay out a program for 
investigation and either handle the problem itself, turn it over to one of its exist- 
ing Subcommittees, or set up a new Subcommittee specifically for consideration 
of this problem. 

After thorough investigation and study of the project, the Subcommittee will 
make its report to the Basic Committee which will then report its recommenda- 
tions to the Research Council. The Research Council will determine final disposi- 
tion of the matter. 

If the subject of the report is of industry-wide interest it may be published for 
general circulation, or if of specialized interest to only a small group within the 
industry it may be distributed upon a restricted basis to only those interested 
in that particular subject. 

The Committees may be as compact and as streamlined as is consistent with 
proper operation, inasmuch as the Research Council and the Basic Committees, 
with their representation from all participating companies, will provide a broad, 
overall, industry viewpoint and supervision. 



DAN CLARK 
ROBERT DEGRASSE 
MERRITT GERSTAD 



HARRY CUNNINGHAM 
FRANK C. GILBERT 



FRED GAGE 
MICHAEL LESHING 



FRED ALBIN 
JOHN FULTON 



BASIC COMMITTEES 

CINEMATOGRAPHIC 

JOHN ARNOLD, Chairman 
C. ROY HUNTER 
ROY SEAWRIGHT 

CINE-TECHNICAL 

GROVER LAUBE, Chairman 
EMIL OSTER 
FRANK YOUNG 

LABORATORY 

J. M. NICKOLAUS, Chairman 
GEORGE SEID 

OPTICAL 

BURTON F. MILLER, Chairman 
GROVER LAUBE 
JOHN LIVADARY 
WILLIAM DRAPER 



WILLIAM THOMAS 
JOSPEH VALENTINE 
JOSEPH WALKER 



AL TONDREAU 
A. G. WISE 



SIDNEY SOLOW 
RAY WILKINSON 



WILBUR SILVERTOOTH 
W. B. SLAUGHTER, JR. 



108 SOCIETY ANNOUNCEMENTS 

SOUND 

LOREN RYDER, Chairman 

LAWRENCE AICHOLTZ WILLIAM MUELLER ELMER RAGUSE 

C. W. FAULKNER CLEM PORTMAN GORDON SAWYER 

WESLEY C. MILLER S. J. TWINING 

General direction of the entire program will be in the hands of the Research 
Council, the membership of which consists of one representative from each studio 
sponsoring the Council, in addition to the Chairman, as follows: John Aalberg, 
RKO Radio; Bernard B. Brown, Universal; Farciot Edouart, Paramount; 
E. H. Hansen, 20th Century-Fox; Nathan Levinson, Warner Brothers; John 
Livadary, Columbia; Thomas Moulton, Samuel Goldwyn; Elmer Raguse, Hal 
Roach; Douglas Shearer, Metro-Gold wyn-May er ; and Gordon S. Mitchell, 
Manager. 



JOURNAL 

OF THE SOCIETY OF 

MOTION PICTURE ENGINEERS 

Volume XXXV August, 1940 



CONTENTS 

Page 

The Control of Sound in Theaters and Preview Rooms 

C. C. POTWIN 111 

An Investigation of the Influence of the Negative and Positive 

Materials on Ground Noise 

O. SANDVIK AND W. K. GRIMWOOD 126 

Filtering Factors of the Magnetic Drive 

R. O. DREW AND E. W. KELLOGG 138 

Current Practices in Blooping Sound-Film 

W. H. OFFENHAUSER, JR. 165 

Optimum Load Impedance for Triode Amplifiers Employing 
Feedback BURTON F. MILLER 172 

A Precision Integrating-Sphere Densitometer 

J. G. FRAYNE AND G. R. CRANE 184 

New Motion Picture Apparatus 

Recording and Reproducing Square Waves D. CANADY 201 

Professional 16-Mm Recording Equipment D. CANADY 207 

Current Literature 212 

Fall Convention at Hollywood, Calif., Oct. 21st-25th, inclusive 214 



JOURNAL 

OF THE SOCIETY OF 

MOTION PICTURE ENGINEERS 



SYLVAN HARRIS, EDITOR 

Board of Editors 
J. I. CRABTRBB, Chairman 

A. N. GOLDSMITH A. C. HARDY T. E. SHBA 

J. G. FRAYNB L. A. JONBS G. E. MATTHBWS 

A. C. DOWNES E. W. KELLOGG 



Subscription to non-members, $8.00 per annum ; to members, $5.00 per annum, 
included in their annual membership dues; single copies, $1.00. A discount 
on subscription or single copies of 15 per cent is allowed to accredited agencies. 
Order from the Society of Motion Picture Engineers, Inc., 20th and Northampton 
Sts., Easton, Pa., or Hotel Pennsylvania, New York, N. Y. 
Published monthly at Easton, Pa., by the Society of Motion Picture Engineers. 

Publication Office, 20th & Northampton Sts., Easton, Pa. 
General and Editorial Office, Hotel Pennsylvania, New York, N. Y. 

West Coast Office, Suite 226, Equitable Bldg., Hollywood, Calif. 
Entered as second class matter January 15, 1930, at the Post Office at Easton, 
Pa., under the Act of March 3, 1879. Copyrighted, 1940, by the Society of 
Motion Picture Engineers, Inc. 

Papers appearing in this Journal may be reprinted, abstracted, or abridged 
provided credit is given to the Journal of the Society of Motion Picture Engineers 
and to the author, or authors, of the papers in question. Exact reference as to 
the volume, number, and page of the Journal must be given. The Society is not 
responsible for statements made by authors. 



OFFICERS OF THE SOCIETY 

* President: E. A. WILLIFORD, 30 East 42nd St., New York, N. Y. 

* Past-President: S. K. WOLF. RKO Building, New York, N. Y. 

* Executive Vice-President: N. LEVINSON, Burbank, Calif. 

** Engineering Vice-President: D. E. HYNDMAN, 350 Madison Ave., New York, 
N. Y. 

* Editorial Vice-President: J. I. CRABTREB, Kodak Park, Rochester, N. Y. 

** Financial Vice-President: A. S. DICKINSON, 28 W. 44th St., New York, N. Y. 

* Convention Vice-President: W. C. KUNZMANN, Box 6087, Cleveland, Ohio. 

* Secretary: J. FRANK. JR., 356 W. 44th St., New York, N. Y. 

* Treasurer: R. O. STROCK, 35 11 35th St., Astoria, Long Island, N. Y. 

GOVERNORS 

* M. C. BATSEL, Front and Market Sts., Camden, N. J. 

* J. A. DUBRAY, 1801 Larchmont Ave., Chicago, 111. 
** A. N. GOLDSMITH, 580 Fifth Ave., New York, N. Y. 
** H. GRIFFIN, 90 Gold St., New York, N. Y. 

* P. J. LARSEN, 29 S. Munn Ave., East Orange, N. J. 

* L. L. RYDER, 5451 Marathon St., Hollywood, Calif. 

** A. C. HARDY, Massachusetts Institute of Technology, Cambridge, Mass. 

* H. G. TASKER, 5451 Marathon St., Hollywood, Calif. 



* Term expires December 31, 1940. 
** Term expires December 31, 1941. 



THE CONTROL OF SOUND IN THEATERS 
AND PREVIEW ROOMS* 



C. C. POTWIN** 



Summary. Acoustical science can now be applied to better advantage than ever 
before in the planning of modern motion picture theaters. A broader understanding of 
the purposes and principles of acoustical design and treatment is needed, however, 
to make this application universal. The Society is in a position to do much toward 
fulfilling this need. 

Greater attention should be given to the design and development of the basic theater 
structure. The shaping of surfaces for the control of sound reflections is effective and 
can be kept within a desirable architectural limit. Furthermore, such shaping can be 
made to function successfully if the basic design is developed to control reverberation. 

The all too prevalent idea that "the more acoustical material used, the better the 
results" should be discouraged. Acoustical materials can be used more efficiently if 
they are distributed asymmetrically with due regard to the geometry of the reflecting 
surfaces. In general, they should not be concentrated in large compact areas on single 
surfaces. This principle of treatment and its effect upon the acoustical characteristics 
of theaters is discussed. 

Instrumental measurements of the effect of surface parallelism upon the frequency 
reverberation characteristic of a rectangular room are shown. The results are of par- 
ticular interest with respect to the acoustical treatment of preview rooms. 

A principal unit of the sound transmission system in motion picture 
theaters can now be efficiently controlled. This unit is the path 
through which sound travels from the loud speakers to the ears of an 
audience in other words, the auditorium the most expensive single 
unit of the sound transmission system. 

In 1929 and 1930, when between 50 and 100 theaters were being 
equipped for sound every week, it was often difficult to convince 
exhibitors of the need for good acoustics. Sound was considered a 
novelty by some; to others good acoustics meant too little to come 
within the sphere of practical necessity. It was not long, however, 
before the novelty wore off and efforts were made to improve sound 
quality in theaters. The exhibitor, sharing in these efforts, began 

* Presented at the 1940 Spring Meeting at Atlantic City, N. J. ; received June 
8, 1940. 

** Electrical Research Products, Inc., New York, N. Y. 

Ill 



112 C. C. POTWIN [J. S. M. P. E. 

seriously to consider improving the acoustical conditions of the im- 
portant transmission link that he furnished. 

Corrective materials were installed in many existing theaters. The 
significant point, however, is that a number of new theaters were 
built without consideration of acoustics and were admittedly not so 
successful as many of the older theaters that had been corrected. 
This led to the rather general belief that sound absorption quantita- 
tively was the only factor in acoustical planning. Architectural 
practices were therefore developed that resulted in the installation of 
excessive amounts of corrective materials. These practices are still 
being followed to a very large extent in theater planning. They 
should now be reversed, and theaters should be shaped fundamentally 
for good acoustics. 

Experience has proved that uneven or irregular surfaces, if properly 
designed, contribute basically to good acoustics. The idea that 
such surfaces have a definite effect upon sound is by no means a new 
theory. As early as 1910, Professor Wallace Sabine recognized their 
value. 1 He pointed out that a coffered ceiling tended to break up or 
disperse sound, and that if the coffers were varied in size and depth 
they would have an even greater effect. His early findings established 
a basis for recent developments and refinements in the use of acousti- 
cal form. 

One may wonder why we continue to stress the importance of 
acoustical shaping for theaters. Its value is reiterated only because 
the results achieved are superior to those obtained through the use 
of excessive amounts of absorbing materials. Proper shaping reduces 
room resonances by distributing the eigentones and permits a greater 
proportion of the reflected sound to be absorbed in the audience area. 

It is interesting to note that several of the very best theaters in 
New York do not have one square-inch of absorbing material on the 
walls or ceiling. In these theaters, surfaces designed to conform with 
architectural styles of the past are so ornate and consequently so 
irregular in form that they effect a rapid dispersion or scattering of 
sound reflections. No doubt many theaters throughout the country, 
both of large and small seating capacities, fall into this class. 

Present trends in design are toward the use of simple interior 
treatments, involving little or no ornamentation. The large plain 
surfaces characteristic of these modern designs tend to produce echoes 
and allow sound to be reflected many times before it dies away to 
inaudibility. Acoustical shaping, based on the development of wall 



Aug., 1940] 



THE CONTROL OF SOUND 



113 



contours rather than on the use of ornamentation, controls these reflec- 
tions and obviates the need for excessive sound absorption to accom- 
plish a similar effect. Architects tell us that this shaping not only 




J 



PLAN 



AAA/VWWV DRAPING 



BAFFLES 



FOLDING DOORS 




SECTION 




100 1,000 10,000 

FREQUENCY IN CYCLES PER SECOND 

FIG. 1. Example of undesirable effect of plane parallel surfaces. 

affords a basis for functional interior design in many instances, but 
can often be blended very well with modern decorative treatments. 

Fig. 1 is an example of the undesirable effect of plane parallel sur- 
faces upon the acoustical characteristics of a rectangular room used 
for sound pictures. Considering the proportions of this room as a 



114 C. C. POTWIN [J. S. M. P. E. 

whole, the length was somewhat excessive and the ceiling height too 
low. Sliding doors were standard equipment for the room, and inas- 
much as the group to be accommodated would not exceed 35 persons, 
it was decided to close these doors partially in order to reduce the ap- 
parent volume, leaving an opening only large enough for projection of 
the picture. 

The coupled room effect 2 which might have produced a feedback 
of reverberation from area Y behind the opening was minimized by 
the use of sound-absorbing baffles of rock wool and heavy draping ma- 
terial, arranged as shown in the figure. Measurements indicated that 
with the acoustical baffling in place no undesirable interference 
phenomena were encountered from this section. 

The next and most significant part of the problem was the acoustical 
treatment of area X, the listening space. There were three obvious 
defects contributing basically to poor acoustics within this half of 
the room : 

(1) The space was generally too live for good sound reproduction. 

(2) The excessively low ceiling produced an acoustical image, or gave the il- 
lusion that sound originated at a point on the ceiling in front of the screen; and 

(5) A flutter-echo effect, caused by repeated sound reflections between the ceil- 
ing and floor, was so severe that it gave a ringing tone to speech and distorted 
sound from the reproducing system. 

The architectural design of the room limited acoustical treatment 
to the use of draping materials. The amount required for the flat 
wall areas was predetermined and installed. This tended to reduce 
the reverberation, but accentuated the flutter-echo. Acoustical 
measurements were made to determine the nature of the flutter-echo 
and the extent to which the additional sound absorption required to 
overcome this effect might be limited to small areas in order to avoid 
an over-damped condition. The results are shown on the graph in 
Fig. 1. 

For the measurements the sound source was positioned on the stage 
and the microphones were placed in the seating area. Curve A (Fig. 
1), taken with the draping material installed on the walls but without 
draping on the ceiling, shows a sharp peak at 400 cps caused by the 
flutter-echo. A rug with heavy lining material placed on the floor in 
front of the seats and covering a part of the area under the seats had 
practically no effect upon the 400-cycle peak. 

A drape hung in a horizontal position one foot below the ceiling, 
at a point between the seating area and the stage, gave the result 



Aug., 1940] THE CONTROL OF SOUND 115 

shown as curve B (Fig. 1). Here the 400-cycle peak is eliminated, 
but there is now excessive absorption at the high frequencies. Obvi- 
ously, the ideal material for the ceiling treatment would be one having 
its maximum absorption at about 400 cycles. Yet with such a ma- 
terial the acoustical image caused by short-path reflections from the 
ceiling would still persist. 

A fabric with a quilted backing and a hard surfaced facing was 
finally selected as most suitable. It damped out the low-frequency 
peaks and gave back a part of the desired liveness at the high fre- 
quencies. 

The significant points in this analysis are : 

(1) If the ceiling had been designed out of parallel with the floor, the flutter- 
echo would not have been produced. 

(2} By proper shaping of the ceiling, the reflections causing the acoustical image 
could have been either dispersed or directed away from the listening areas where 
they proved annoying. 

(5) On this basis, excessive absorbing material would not have been required 
to correct these defects. 

Admittedly, this represents an extreme case so far as the theater is 
concerned. The ceiling and floor are not usually parallel in theaters, 
and upholstered seats covering practically the entire floor area help 
both to break up and to absorb sound in the vertical plane. For this 
reason the example is perhaps more directly comparable to the 
average preview room, where only a part of the floor area is normally 
used for seating and the problems of room resonance and control of 
discrete reflections are sometimes even more critical than in the 
theater. 

The ceiling-to-floor condition, however, is comparable to parallel 
walls in the theater, where one or more frequencies may be accentu- 
ated by multiple reflections occurring between these surfaces. If the 
ceiling of the theater is completely treated and the side walls are 
neither acoustically shaped nor treated, the flutter-echo may occur 
between the walls and may be accentuated in the same manner as 
the ceiling-to-floor condition was in this example. 

The type of irregular surface most desirable for use in breaking up 
or distributing sound reflections in a theater or preview room de- 
pends upon the angles and position of the walls, the ceiling, and the 
seating area, as seen from the source of sound. The shaping may fol- 
low a number of different forms, all of which can be developed for 
artistic value. Angular and splayed forms, carried vertically from the 



116 C. C. POTWIN [J. S. M. P. E. 

floor or from a suitable wainscot to the ceiling, have been most often 
used in the past. Experience indicates that convexly curved forms 
and angular or splayed surfaces running horizontally instead of 
vertically, or combined with vertical shaping, can also be used with 
equally successful results. 

A projection of 1 inch to the running foot is sufficient in most cases 
for the design of angular or convex surfaces. Sharp angles, develop- 
ing pockets, are not only too severe architecturally but frequently 
produce resonant cavities. 

When angular forms are used, the points of projection should be 
directly opposite one another on facing surfaces. Otherwise it may 
happen that the sides of two opposite angles will actually be parallel. 

Where a rear wall or a balcony edge is sloped or otherwise shaped 
to prevent echoes, a projection of more than 1 inch to the running foot 
is usually required. In these cases the shaping should be planned so 
that the first reflection from a point at the extreme upper edge of 
the surface strikes the audience at a distance preferably not greater 
than 25 feet in front of the reflecting surface. 

In connection with the design or remodelling of theaters and pre- 
view rooms having low ceilings it is often possible to shape the ceiling 
so as to create an acoustical effect of increased height. If this shaping 
is carefully plannned architecturally a similar visual effect may also 
be obtained. 

The question frequently arises, "Is it possible to design a modern 
theater for optimum hearing conditions without using acoustical- 
materials?" This can be done if the theater is shaped originally so 
that multiple reflections are eliminated, discrete reflections of high 
intensity do not reach the audience area too quickly, and the forma- 
tion of echoes is prevented. However, proper shaping alone is not 
enough. Fundamental consideration must also be given to the factor 
of limiting cubic -foot volume per seat in design. 

Fig. 2 shows desirable limits of cubic-foot volume in relation to 
seating, for modern theater auditoriums, based upon controlling 
sound reflections by internal surface shaping. These limits have been 
developed as a result of empirical practice, and assume (1) the use of 
upholstered seats with a spring or rubber cushioned bottom and pad- 
ded back, (2) fully carpeted aisles, and (3) furred construction of 
walls and ceiling for low-frequency absorption. 

The broken curve is considered generally from past experience to be 
a maximum practical limit for the auditorium structure. In most 



Aug., 1940] 



THE CONTROL OF SOUND 



117 



cases a small amount of acoustical material properly distributed will 
be required for these larger volumes. Cubages in excess of this limit 
are rapidly leading away from rather than toward economy in 
auditorium design. 

In planning for the control of cubic-foot volume, it is usually more 
difficult to deal with single-floor houses than with those having a 
balcony. This can readily be understood from the fact that in the 
balcony house a greater amount of structural break-up is provided, 
to begin with, at the rear of the auditorium. However, there are 



DESIRABLE LIMITS OF CUBIC FOOT 
EAT 



77 /////// /V///I 
DESIGN LIMITS 




250 



1500 



789 
500 1000 

NUMBER OF SEATS 

FIG. 2. Desirable limits of cubic-foot volume in relation to seat- 
ing, based upon control by internal surface shaping. 



possibilities in the acoustical design of modern single-floor houses 
that have not yet been developed. For example, ceilings that slope 
or step down rather abruptly at the rear and sides, and walls that con- 
verge slightly toward the rear, offer means of controlling cubic-foot 
volume and reducing rear wall area in design. 

Since the time of reverberation at various frequencies is related 
directly to cubic-foot volume and to quantity and quality of sound 
absorption, it seems advisable at this point to discuss briefly the 
amount and the frequency characteristic of the reverberation de- 
sirable for motion picture theaters. There is nearly universal agree- 



118 C. C. POTWIN [J. S. M. P. E. 

ment among engineering groups as to the desirable time of reverbera- 
tion at 512 cycles per second. Curve A in Fig. 3 is based upon our 
experience, and shows desirable reverberation times in relation to 
volume at this particular frequency. 

The desirable times of reverberation for frequencies below 512 
cps require further study. The optimal frequency characteristic 
derived from theoretical considerations by MacNair 3 and shown as 
curve B in Fig. 3, corrected at the high frequencies on the basis of the 
Fletcher and Munson data, 4 has been found to produce very good re- 
sults in theaters having volumes greater than 300,000 cubic-feet. 
However, a more nearly flat characteristic at the low frequencies seems 
to produce the best results in theaters or preview rooms having 
volumes less than 50,000 cubic-feet. 

Curve C in Fig. 3 is based upon empirical studies and design prac- 
tice, 5 and shows ratios of reverberation time in per cent at 128 cycles 
to the time at 512 cycles, as a function of size. It will be noted that 
while the greatest departures from the MacNair values are for rooms 
of 10,000 cubic-feet or less, there is no appreciable departure for 
theaters of very large volumes. Curve D in Fig. 3 is a similar expres- 
sion of the values at 256 cycles. 

A number of successful theaters and preview rooms have been 
planned in accordance with these data. It seems possible that a 
reconsideration of desirable times at 512 cycles may also be necessary 
in the future, since experience indicates that higher reverberation 
times can be used when more attention is given to the control of sound 
by design and surface shaping. 

While it is possible to plan theaters in such a way that acoustical 
materials are not necessarily required, it would be very optimistic 
to expect that such a practice might be adopted universally. Acousti- 
cal materials will no doubt generally be needed in modern theaters of 
large seating capacity. They may also be required in smaller theaters 
where the architect prefers the use of plain unbroken surfaces to 
studied acoustical forms. Whatever the case may be, these materials 
can now be used to much better advantage than they have been in 
the past. 

It has been common practice to cover surfaces almost completely 
with acoustical materials, or to confine these materials to single sur- 
faces such as the ceiling. Apparently this has been done for two 
reasons: first, because it seems easier architecturally to cover an 
entire surface than only selected parts of a surface, and second, be- 



Aug., 1940] 



THE CONTROL OF SOUND 



119 



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c 
.2 

"o 



!N30d3d Nl ZIS IV iVHi 01 AON3n03dd 
ANV IV 3WI1 NOIlVd38a3A3 JO OllVb 



ZIS 01 <">83I IV 

3WI1 NOIlVH3BH3A3a JO OllVd 



120 



C. C. POTWIN 



[J. S. M. P. E. 



cause the importance and value of distributing materials have not 
been fully understood or appreciated. 

Actually, absorbing materials prove most effective when they are 
used in small quantities non-uniformly, instead of being concentrated 
in large compact masses on single surfaces. 6 This method of acousti- 
cal treatment was first tried and the results observed in sound record- 
ing studios and scoring stages. With the use of materials non-uni- 
formly distributed, leaving some areas for reflection on all surfaces, 




FIG. 4. Typical sound recording studio before installation of decorative 
coverings over acoustical material. 

the quality of sound as picked up by the microphone was excep- 
tionally pleasing and natural, without the effects of "deadness" so 
characteristic of many rooms of this type. Reverberation measure- 
ments made in these spaces showed a practically logarithmic decay 
for all frequencies, modulated slightly by a large number of low-in- 
tensity pattern changes but free of any high-intensity ones. These 
results checked very well with the types of sound decay measured 
in other spaces noted for their excellent acoustical properties. It ap- 
peared that the background reverberation should be made up of long- 
path, or what have been termed "around-the-room," reflections, and 



Aug., 1940] THE CONTROL OF SOUND 121 

that the discrete or short-path reflections of high intensity should be 
either absorbed quickly or directed away from the microphone area. 
This conclusion was also supported by subjective reactions as to the 
most pleasing types of sound decay. 

Fig. 4 is a photograph of a typical sound recording studio, taken 
before any final decorative covering was installed over the acoustical 
material. Particular attention is directed to the arrangement of 
acoustical treatment and to the fact that sound reflecting areas, 
varying in size and arrangement, are retained on all surfaces around 
the absorbing panels. The absorbing material on the upper wall 
areas is widely and non-uniformly distributed with respect to op- 
posite sides and ends of the room, in order that the long-path reflec- 
tions for pleasing background reverberation may be established and 
maintained. The treatment is more closely spaced on the lower wall 
areas in order to prevent discrete reflections from reaching the micro- 
phone. In this case the non-symmetrical arrangement of acoustical 
material has been coordinated with angular contours on the walls 
and ceiling. 

Recently this new method of treatment has been used with equally 
successful results where acoustical materials were required in motion 
picture theaters. If, in addition, it is combined with irregular shap- 
ing of surfaces the quantity of material needed is usually less than 
that required for theaters of regular form. 

Several other significant points in connection with this method of 
treatment have a definite bearing upon the acoustical characteristics 
of the motion picture theater. Low-frequency reverberation, or 
boominess, has been a prime offender in many instances. Measure- 
ments show that when materials are distributed non-uniformly their 
effective absorption is increased at the low frequencies. 

This method of treatment also leads to economy in theater construc- 
tion. It is certainly more economical to use less material and distrib- 
ute it efficiently than it is to use large amounts and possibly produce 
"dead" conditions in a theater. 

The fact that this arrangement of treatment does not look especially 
artistic at first glance should not discredit its possible use if intel- 
ligently handled from the decorative viewpoint. Although covering 
materials have been used in the past to disguise the irregular distribu- 
tion, architects tell us that they see no reason why decorative pat- 
terns following such a scheme can not be worked out directly on a 
surface so as to give a pleasing effect. 



122 



C. C. POTWIN 



[J. S. M. P. E. 



Fig. 5 shows a section and interior view of a theater recently com- 
pleted at the University of Wisconsin. This theater seats 1400 per- 
sons and is used both for sound motion pictures and stage productions. 
The walls consist of a series of convexly curved forms coordinated with 
a non-symmetrical arrangement of sound-absorbing material. The 





FIG. 5. Wisconsin Union Theater, University of Wisconsin. (Upper} 
Section showing outline form and distribution of acoustical treatment; 
(lower) panorama view of interior. 



ceiling follows a gradually decreasing curvature from the stage open- 
ing to the rear of the balcony. 

The arrangement of acoustical panels along one side wall is shown 
on the section drawing. These panels are non-symmetrically spaced 
with respect to the panels on the opposite side. They are covered 
with a perforated board installed flush with the hard plaster surface, 
and are painted a matching color. 



Aug., 1940] THE CONTROL OF SOUND 123 

The balcony rear wall is both acoustically shaped and non-uni- 
formly treated to prevent echoes; the balcony edge is convexly 
rounded to scatter direct reflections; the balcony soffit is sloped to 
strengthen the sound level under the balcony; and a sliding glass 
partition at the rear is tilted so that reflections from this surface will 
not reach the forward seating area. 

It is interesting to note that although this theater has an enclosed 
volume of almost 300,000 cubic-feet, only 750 sabines of acoustical 
material are used. In spite of this, the percentage articulation at the 
extreme rear of the balcony under empty house conditions is 84 per 
cent. 7 

This represents a theater of large seating capacity, where a small 
amount of absorbing material was needed to complete the acoustical 
design. For an example of a theater of more nearly average size, 
where no acoustical material was used, attention is directed to a 
theater design described at the Detroit convention in 1938. 8 This 
theater seats approximately 900 persons and is located in Hamden, 
Conn. The side walls consist of a series of angular forms running hori- 
zontally instead of vertically, the rear wall is convexly curved, and the 
reverberation time is controlled by limiting the cubic-foot volume. 
No measurements have been made as yet, but listening tests indicate 
that sound reflections are being efficiently controlled by the interior 
surface shaping. 

In conclusion, the author wishes again to emphasize the importance 
of the auditorium as a part of the complete sound transmission system. 
It either serves to support the impression the director chose to convey 
through the medium of sound or it tends to destroy that impression. 
The acoustical design of theaters and the strategic use of absorbing 
materials, properly coordinated with the acoustical characteristics of 
the sound-reproducing system, can contribute much to the psycho- 
logical effect of "carrying the listener into the scene." 

REFERENCES 

1 SABINE, W. C.: "Collected Papers on Acoustics," Harvard University Press, 
Cambridge, Mass. 

2 EYRING, C. F.: "Reverberation Time Measurements in Coupled Rooms," 
J. Acoust. Soc. Amer., 3 (1931), p. 181. 

3 MACNAIR, W. A.: "Optimum Reverberation Time for Auditoriums," J. 
Acoust. Soc. Amer., 1 (1930), p. 242. 

4 FLETCHER, H., AND MUNSON, W. A.: "Loudness, Its Definition, Measurement 
and Calculation," /. Acoust. Soc. Amer., 5 (1933), p. 82. 



124 C. C. POTWIN [J. S. M. P. E. 

6 MAXFIELD, J. P., AND POTWIN, C. C.: "Planning Functionally for Good 
Acoustics," /. Acoust. Soc. Amer., 11 (1940), p. 383. 

6 POTWIN, C. C., AND MAXFIELD, J. P.: "A Modern Concept of Acoustical 
Design," /. Acoust. Soc. Amer., 11 (1939), p. 48. 

7 FLETCHER, H., AND STEINBERG, J. C.: "Articulation Testing Methods," Bell 
Syst. Tech. J. (Oct., 1929); also J. Acoust. Soc. Amer. (Supplement to Jan., 1930). 

8 POTWIN, C. C., AND SCHLANGER, B.: "Coordinating Acoustics and Architec- 
ture in the Design of the Motion Picture Theater," /. Soc. Mot. Pict. Eng., XXXII 
(1939), p. 156. 

DISCUSSION 

MR. KELLOGG: I believe Professor Cook of Princeton University had some 
ideas about the shaping of surfaces to get the optimum result. Are his ideas being 
followed and found useful? 

MR. POTWIN: Professor Cook did some experimental work on the shaping of 
ceilings. As a matter of fact, I believe we can go back beyond that, to several 
auditoriums in Europe where ceilings were shaped to take advantage of beneficial 
reflection. Professor Cook's original work was done in connection with a proposed 
new opera house at Philadelphia, in which the ceiling was to be shaped to reflect 
sound to the audience. He has recently carried the scheme further and has super- 
imposed a series of small concave curves on the major curve in the development 
of the cross-sectional form. Such a ceiling is used in the Princeton Playhouse. 

The ceiling of the Wisconsin University Theater which I have shown differs 
from the Cook ceiling in that it is perfectly flat in the cross-section, meeting the 
walls at right angles, and is shaped longitudinally to heighten the acoustical image 
in only the rear half of the balcony. 

MR. KELLOGG: Wasn't it one of Professor Cook's fundamental principles to 
try to avoid any reflection that was more than about 50 feet, or less, behind the 
original sound? 

MR. POTWIN: Yes, such a relation was worked out for the entire seating area 
beyond a point approximately 30 feet from the stage. This was done for a single- 
floor house of the stadium type, where the seating area sloped up rather sharply 
toward the rear. 

MR. KELLOGG: In Fig. 1 you illustrated something that has puzzled me. If 
you assume that the sound starts from a point about the center of the screen, 
and you draw a diagram of its paths, assuming that it will be reflected from each 
surface at the same angle at which it strikes the surface, there does not appear 
to be any action that would eventually establish a system of waves going straight 
up and down. How, then, does the flutter between floor and ceiling get started? 
It has occurred to me that it might be a grating effect. The tone that you re- 
ported as being reinforced by this flutter was 400 cps. The spacing of the seats 
is not very far from Y 4 oo seconds in travelling time. Do you think that the rows 
of seats might have acted as a diffraction grating? 

MR. POTWIN : Not in this case, because there was an open area of approximately 
20 feet between the stage and the first row of seats. 

MR. RYDER: The same phenomenon has been observed out west. There is a 
small theater in the San Fernando Valley where it was felt that the seating ar- 



Aug., 1940] THE CONTROL OF SOUND 125 

rangement had reinforced the frequency band at approximately 400 cycles. The 
effect was not definitely the flutter-echo effect that sharp click-back that you 
get from a flutter-echo, but was a tearing-up or too strong a signal in the 400-cycle 
range which tended to disturb the dialog intelligibility. 

MR. POTWIN: The flutter-echo was equally pronounced in this case without 
any seats in the room. 

MR. LUBCKE: Do you believe that the technic you have outlined, notably 
skewed walls and small surfaces of absorption material, would be applicable to 
sound production stages where generally the volume is much greater? 

MR. POTWIN: Very definitely. However, in that case coordinating the dis- 
tribution of acoustical treatment with surface shaping would involve the use of 
much more absorbing material than is usually needed for the theater in view of 
the much larger volume of the enclosed space. 

MR. RICHARDSON: In the Pix theater at White Plains, N. Y., the ceiling curves 
down gradually to the walls, which are perfectly plain and flat. An acoustical 
material was used, and the sound is eminently satisfactory. 

MR. POTWIN: We were consultants to Mr. Schlanger, the architect, in the re- 
modelling of the Pix Theater. It is a very long house, and there would have 
been quite a strong kick-back from the rear wall as a result of the 25-foot increase 
in length. The rear wall was perfectly flat and could not be changed structurally. 
The only additional acoustical treatment installed was a 1-inch rock- wool blanket 
to cover the original acoustical plaster on this surface. The acoustical plaster was 
retained on the ceiling (the side walls were ordinary plaster) and in order to avoid 
bad reflections at the front of the house within the new extension, this entire sec- 
tion was shaped for sound control. 

MR. RICHARDSON: Are you following the same design at Hamden as you did 
in the Pix? 

MR. POTWIN : The Hamden Theater has horizontal angular forms and the Pix 
Theater has vertical angular forms, and they differ in dimensions. 



AN INVESTIGATION OF THE INFLUENCE OF THE 
NEGATIVE AND POSITIVE MATERIALS ON GROUND 

NOISE* 



O. SANDVIK AND W. K. GRIM WOOD** 

Summary. This paper deals with the effect of the negative sound-track upon the 
ground noise of the print. Data are presented showing the influence of negative density 
and negative gamma on print ground noise for fine-, medium-, and coarse-grain 
negative emulsions. 

In the early days of sound recording on film, the noise due to grain 
structure was almost completely obscured by the noise caused by dirt 
and abrasion. When, in 1934, the present authors 1 published a paper 
on ground noise, film handling technic had progressed to a point where 
it was possible to present data on the noise arising from the granular 
structure of the photographic image. 

Since that time further improvements, not only in film handling 
but also in maintaining good contact during the printing operation, 
have made it possible to evaluate with a fair degree of accuracy the 
extent to which the print noise level is dependent on the negative 
grain noise. 

This present investigation of ground noise was undertaken pri- 
marily to determine the degree to which the granularity of the vari- 
able-density sound negative affected that portion of the print ground 
noise which is due to grain structure. 

Three commercially available emulsions, which may be roughly 
classified as fine-, medium-, and coarse-grain emulsions, were chosen 
for negative materials. Each negative material was exposed so as to 
give a series of densities, each fifty feet in length, covering a density 
range of zero to the maximum obtainable with the exposing equip- 
ment used. In those cases where the density was not limited by the 
exposing means, the upper limit of density was chosen as approxi- 
mately 2.0. Such a set of negatives of different densities was made at 

* Presented at the 1940 Spring Meeting at Atlantic City, N. J. ; Communica- 
tion No. 763 from the Kodak Research Laboratories, received May 1, 1940. 
** Eastman Kodak Co., Rochester, N. Y. 

126 



INVESTIGATION OF GROUND NOISE 



127 



several gammas. The negatives were developed on a continuous 
processing machine and printed on a non-slip printer with an unfiltered 
tungsten lamp. Each negative condition of density and gamma was 
printed to a series of densities covering the range of to 2.0. Two 
print materials were used, namely: regular cine positive 1301 and 
the fine-grain master positive material, 1365. Each print material 
was developed to the gamma that would give satisfactory picture 
print contrasts. 

Fig. 1 is a block diagram of the measuring equipment used. R is 
the sound reproducer, employing a standard type of optical system. 






L 
LI MITER 




CATHODE 
RAV 
TUBE 












1 


F 


| 500" 


T 
THERMO 
COUPLE 
METER 


H.RP1LTEP 




|zoo 

p. 


oo w 




FIG. 1. Ground noise measuring equipment. 



The usual coiled-filament lamp is replaced by an 18-ampere ribbon- 
filament lamp to minimize microphonic difficulties. The noise level 
of the reproducer is primarily the "shot effect" noise of the photocell 
and the thermal agitation noise of the photocell coupling resistors. 
The noise level with the reproducer running is less than 1 / 2 db higher 
than with the machine stationary. The minimum ground noise that 
can be measured is determined by the amplifier noise level which is 
75-76 db below the level of a signal produced by a 100 per cent 
modulation of the exciter lamp output. The amplifier is equalized 
to compensate for reproducing losses up to 10,000 cps, so that the 
output of the reproducer for frequencies below 10,000 cps is pro- 
portional to the transmission changes of the film. 



128 



O. SANDVIK AND W. K. GRIMWOOD [J. s. M. P. E. 



F is a high-pass filter of 150 cps, which is used to eliminate errors 
from density variations caused by development effects such as the 96- 
cycle density variation which occurs near the sprocket holes. Trials 
made with a 500-cps high-pass filter indicated that the 96-cycle varia- 
tions were reduced to a negligible value when using the lower cut-off 
filter. The thermocouple meter, T, of 500 ohms resistance, gives a 
true power measurement of the ground noise with a flat frequency 
response between 150 and 10,000 cps. The limiter, L, is designed to 
protect the thermocouple from high-amplitude surges such as might 
be caused by splices or deep abrasions on the film. The cathode-ray 
tube is not used for measuring, but is very valuable in determining 



o 

Q -30 



-40 



THERMOCOUPLE 




IOO IOOO 

FREQUENCY- CYCLES PER SECOND 



FIG. 2. 



Frequency response characteristics of ground noise re- 
producer. 



when noise is present from sources other than the granularity of the 
emulsion. 

The thermocouple input is bridged by a 20-db, 20,000- to 500-ohm 
pad, PI, which goes to the equalizer, E. This equalizer matches the 
standard electrical characteristics for theater reproducers as specified 
by the Academy of Motion Picture Arts and Sciences. 2 From the 
equalizer the signal goes through a 30-db 500-ohm pad, PZ, a 20-db 
500- to 30-ohm matching pad, P 3 , to the noisemeter, N. N is a com- 
mercial noisemeter whose characteristics conform to the specifica- 
tions of the American Standards Association and is used with a fre- 
quency response approximating that of the ear at a loudness level of 
40 db. The noisemeter indication is taken as a rough indication of 
what the ear would hear as film noise in an auditorium. 



Aug., 1940] 



INVESTIGATION OF GROUND NOISE 



129 



Fig. 2 shows the overall response from film transmission to meter 
indication of the two measuring systems. 



RESULTS 



A typical ground noise curve is shown in Fig. 3 where the upper 
curve represents data taken with the thermocouple meter and flat 
frequency response, and the lower curve represents data taken with 



-4-0 



.. 



60 



TO 



80- 




0.5 



I.O 



2..O 



PRINT DEMSITV 
FIG. 3. Print ground noise vs. print density. 

the noisemeter and a weighted frequency response. At zero print 
density the noise has a measurable value (though variable from one 
test film to another) which is due to abrasions, developer sludge, and 
base imperfections, and does not indicate grain noise since there are 
no silver grains present. As the density is increased to measurable 
values, the noise due to the silver grains increases and soon obscures 
the decreasing base and abrasion noise. The noise due to grains 
reaches a maximum at a diffuse density of approximately 0.2 above 
which the noise decreases. Above a density of 0.4 to 0.5 the noise 



130 



O. SANDVIK AND W. K. GRIMWOOD [j. s. M. p. E. 



decreases linearly with the increase of density until the density be- 
comes so high that amplifier noise begins to affect the readings as 
indicated by the point at which the noise curves begin to bend over 
and finally become asymptotic to the density axis at a level deter- 
mined by the amplifier noise; in these measurements, this occurred 
at a level of 75 decibels. 



O -40 

\ 

O 50 



^* 

8 TO 



THERMOCOUPLE 



NO ISEMETEC 



O O-5 t.Q 

NEGATIVE GAMMA 
FIG. 4. Print ground noise 
vs. negative gamma. 

Negative: 1359. Density 

= 0.50. Developer B. 
Print: 1301. Density = 
0.65. Gamma = 2.1. De- 
veloper D-16. 



40 



50 



60 



THERMOCOUPLE 



N018EMETER 



0.5 



1.0 



FIG. 5. 



NEGATIVE GAMMA, 

Print ground noise vs. negative 
gamma. 



Negative: 1357. Density = 0.50. 

Developer C. 

Print: 1301. Density = 0.65. Gamma 
= 2.2. Developer D-16. 



The original measurements were of print ground noise as a function 
of print density for a fixed negative gamma and density. A large 
number of such curves were obtained, each curve corresponding to a 
different negative condition. By replotting these curves, other fami- 
lies of curves were obtained showing the print noise, at a given print 
density, as a function of either the negative density or the negative 
gamma. Fig. 4 is one such curve in which the ground noise of a 
normal print is plotted against negative gamma for a chosen negative 
and print density. It will be seen that the print noise is independent 



Aug., 1940] 



INVESTIGATION OF GROUND NOISE 



131 



of the negative gamma for values of gamma lying within the range 
normally used in sound recording. It will be noted further that the 
print noise is independent of the negative densities for values of 
negative densities below 1.0 at the normal negative gamma of 0.35. 

Fig. 5 presents similar data for negatives developed in a higher 
potential developer than those of Fig. 4. Here the curves have a 



4-O 



k 

3* 50 



Y 60 
(9 



THERMOCOUPLE 



NOISEMETER 



O O.5 IO 

NEGATIVE GAMMA 

FIG. 6. Print ground noise 
vs. negative gamma. 

Negative: 1359. Density 
= 0.50. Developer B. 
Print: 1365. Density = 
0.65. Gamma = 2.2. De- 
veloper D-16. 



40 



Ul 




0% 




TO 



THERMOCOUPLE 



NO\SEMETER 



1.5 



O 0.5 LO 

NEGATIVE GAMMA 
FIG. 7. Print ground noise vs. negative 
gamma. 

Negative: 1365. Density = 0.50. 

Developer A. 

Print: 1365. Density = 0.65. Gamma 
= 2.5. Developer D-16. 



slight upward slope, indicating that the negative is contributing to 
the print noise. 

The data in Fig. 6 are similar to those in Fig. 4 except that the 
prints were made on the fine-grain master positive film instead of 
regular cine positive. It will be noted that, because of the finer-grain 
positive emulsion, the noise level of the print is no longer independent 
of the negative sensitometric conditions. These conditions, especially 
the negative gamma, now have a decided effect on the print noise. 
For the range of densities and gamma normally used in sound record- 



132 O. SANDVIK AND W. K. GRIMWOOD [j. s. M. p. E. 

ing, the absolute value of the print noise is appreciably lower for the 
fine-grain master positive print than for prints made on regular cine 
positive film. The fact that the negative does contribute to the noise 
level of a fine-grain print, however, indicates that a finer-grain nega- 
tive would result in still further improvement in noise level. That 
such is actually the case is shown by Fig. 7 which gives the noise level 
of a fine-grain print as a function of the gamma of a fine-grain nega- 
tive. The print noise is again only slightly dependent on negative 
conditions and its absolute value is of the order of 5 db less than that 
for normal sound-recording negatives and cine positive prints. This 
same fine-grain negative, when printed on regular cine positive stock, 
gives a print noise level which is almost completely independent of 
the negative density and gamma and is very nearly of the same 

TABLE I 

Noise Levels of Negative and Positive Materials 

Noise Level 
(thermocouple) 

-60.5 
-56.7 
-55.4 
-46.3 
-49.3 
-54.0 

absolute level as a cine positive print of the medium-grain negative. 
Hence, there is little or no improvement of noise level to be expected 
from using a fine-grain negative material in combination with a 
medium-grain size print material. 

Further corroboration of the influence of the negative on print 
noise is found in data for prints from a coarse-grain negative material. 
Prints from this negative show an increase of approximately 1.5 db 
for every 0.2 increase in gamma. Using this type of negative material, 
no improvement in the noise level is found by the use of a fine-grain 
print material. 

Data on the noise levels of negative alone and positive material 
alone are given in Table I. These data are not given as accurate 
values of noise level since that may vary somewhat according to the 
composition and age of the developer, but are intended to indicate 
approximate values. The data show that the noise level of the fine- 
grain emulsion used as a variable-density sound-recording negative 



Material 


Developer 


Density 


Gamma 


Fine grain 


A 


0.50 


0.35 


Medium grain 


C 


0.50 


0.35 


Medium grain 


B 


0.50 


0.35 


Coarse grain 


C 


0.50 


0.35 


Cine positive 


D-16 


0.65 


2.1 


Fine grain 


D-16 


0.65 


2.4 



Aug., 1940] 



INVESTIGATION OF GROUND NOISE 



133 



material is approximately 4 db less than that of the regular negative 
emulsion under the corresponding sensitometric conditions. Simi- 
larly, the noise level of the fine-grain emulsion used as a positive ma- 
terial is about 5 db less than that of regular cine positive under the 
corresponding sensitometric conditions. The noise level of the fine- 
grain emulsion, when exposed and processed to conform to the 
normal sensitometric conditions of a variable-density negative, is 
approximately 6 db lower than the noise level of the same emulsion 
when exposed and processed in accordance with the normal print con- 
ditions. This indicates that, for optimum print noise level, when the 
same material is used for both negative and print, the negative 

TABLE n 

Comparative Noise Levels of Normal Prints 



Material 


Developer 


Density 


Gamma 


Noise 


Level 


Neg. 


Print 


Neg. 


Print 


Neg. 


Print 


Neg. 


Print 


Thermo- 
couple 


Noise- 
meter 


1365 


1365 


A 


D-16 


0.50 


0.65 


0.35 


2.26 


-54.3 


-57.6 


1365 


1301 


A 


D-16 


0.50 


0.65 


0.35 


2.14 


-50.0 


-53.2 


1357 


1365 


A 


D-16 


0.51 


0.65 


0.35 


2.26 


-52.7 


-56.0 


1357 


1365 


C 


D-16 


0.51 


0.65 


0.35 


2.36 


-52.2 


-55.8 


1357 


1301 


A 


D-16 


0.51 


0.65 


0.35 


2.20 


-50.2 


-53.9 


1357 


1301 


C 


D-16 


0.51 


0.65 


0.35 


2.14 


-50.2 


-53.7 


1232 


1365 


C 


D-16 


0.50 


0.65 


0.37 


2.24 


-48.3 


-52.7 


1232 


1301 


C 


D-16 


0.50 


0.65 


0.37 


2.20 


-46.9 


-50.3 



should be developed to a higher gamma than is normally used, and 
the print should be developed to a correspondingly lower gamma. 

While the data on any one series of prints are believed to be ac- 
curate, the validity of comparing different sets of prints is question- 
able because it was sometimes necessary to replace the positive de- 
veloper. Furthermore, some of the data indicate that the noise level 
may change appreciably with small changes in the developer through- 
out its normal life. 

To obtain a direct comparison of the noise levels from the types of 
emulsion previously measured, a second set of negatives was made, 
the negative conditions in this case being fixed at a density of 0.50 
and a gamma of 0.35. Each negative was printed to a series of print 
densities, care being taken to handle all prints alike. The results ob- 
tained on this second set are shown in Table II. It will be observed 
that these data check closely with the data in Table III which are 



134 O. SANDVIK AND W. K. GRIMWOOD [J. S. M. p. E. 

taken from curves derived from the complete sets of negatives and 
prints. 

The noise level of a photographic sound recording is but one of 
many factors affecting the general sound quality. When the noise 
level is reduced by the use of fine-grain emulsions, there are simultane- 
ous improvements in the resolution and wave-form of low-modula- 
tion signals, resulting in greater improvement in quality than would 
be expected on the basis of noise measurements alone. 

One method of showing graphically the result of a change in sound 
recording negative and print emulsions is to measure the relation 

TABLE III 

Comparative Noise Levels of Normal Prints 

Emulsion Developer Emulsion Gamma Thermocouple Noisemeter 

1365 A 1365 2.5 -53.7 -57.3 

1365 A 1301 2.2 -49.5 -53.0 

1359 B 1365 2.5 -49.8 -53.5 

1359 B 1301 2.1 -48.0 -52.0 

1357 C 1365 2.5 -51.0 -54.9 

1357 C 1301 2.2 -47.7 -51.6 

1232 C 1365 2.4 -47.7 -51.8 

1232 C 1301 2.0 -47.8 -51.2 

Negative gamma = . 35 
Negative density = . 50 
Print density = 0.65 
Print developer, D-16 

between print output level and recorder input level for several fre- 
quencies. 

Fig. 8 is a graph of such a measurement. The output level cor- 
responding to 100 per cent modulation of the recording light-beam 
has been adjusted to zero for all frequencies. One set of curves repre- 
sents a 1301 print of a 1357 negative, and the other represents a fine- 
grain print of a fine-grain negative. The range of outputs over which 
the output level departs from linearity with the input level by less 
than 2 db is from 6 to 9 db greater for the fine-grain negative and 
print than for the 1357-1301 combination. A more detailed discussion 
of the significance of this type of measurement will be given in a 
later paper. 

In all the data taken there is a constant difference of about 4 db 
between thermocouple readings and the noisemeter measurements. 



Aug., 1940] 



INVESTIGATION OF GROUND NOISE 



135 



In view of the widely different frequency responses used for these two 
measurements, this indicates that the frequency distribution of 
grain noise is the same for the three types of emulsions and over the 
range of sensitometric conditions covered by the measurements. 



NEGATIVE: 1359 OENSITVSO.AA &AVIMA-=O.V 
PRINT : I3OI DENSITY=O.63 <SAMV A>= 



oe.f 




: 1366 DENSITY- 0.43 GAMMVO 35 
PRINT . I3O2 DENSITYrO63 GAMMA*2.6 



O 10 20 30 40 5O 

RECORDER INPUT- DECIBELS BELOW IOO% MODULATION 

FIG. 8. Volume range of variable-density prints. 



More information on the frequency distribution of film noise will be 
presented in a later paper, in which certain aspects of ground noise 
relative to the variable-area type of sound-track will be discussed. 

REFERENCES 

1 SANDVIK, O., HALL, V. C., AND GRIMWOOD, W. K. : "Further Investigation of 
Ground Noise in Photographic Sound Records," /. Soc. Mot. Pict. Eng., XXII 
(Feb., 1934), p. 83. 

2 "Standard Electrical Characteristic for Two Way Reproducing Systems in 
Theaters, Acad. Mot. Pict. Arts & Sci., Techn. Bull., (March 31, 1937). 

3 GOETZ, A., GOULD, W. O., AND DEMBER, A. : "The Objective Measurement of 
the Graininess of Photographic Emulsions," /. Soc. Mot. Pict. Eng., XXXTV 
(March, 1940), p. 279. 



DISCUSSION 

MR. ROBERTS: Have you made any tests on the influence of the type of light- 
source? Is there any difference between a highly collimated light-source, with 
which you probably made these tests, and a very diffused light-source? 

MR. GRIMWOOD: We have not made any tests on the effect of the degree of 
specularity of the light-source. Tests made some years ago with a projection 
printer showed a marked dependence of the frequency response on the diffusion of 



136 O. SANDVIK AND W. K. GRIMWOOD [j. s. M. p. E. 

the light-source, indicating poorer definition with a different source. This would 
lead us to expect that the portion of the print noise due to the negative would be 
less for a diffuse light-source than for a highly specular source. 

MR. McNABB : Has any study been made of the subjective effect of noise, as 
would be occasioned by the response of the human ear? Was a weighting net- 
work inserted in the equipment to approximate the characteristics of the human 
ear? 

MR. GRIMWOOD: We used the weighting network for a loudness level of 40 db 
with the standard noise-meter. That probably represents fairly closely what the 
ear would hear for a continuous noise; but in the case of clicks from abrasion I 
do not believe a noise-meter indication would mean much in terms of what the ear 
actually hears. 

MR. MCNABB: I do not know whether I am right or not in my assumption 
that all noise frequencies are equally objectionable so long as they are equally 
persistent. In broadcasting work, for instance, weighting networks are not used 
in noise-measuring equipment. 

MR. RYDER: In Hollywood we have made quite extensive tests on audience 
reaction to noise. We have introduced the type of background noise that we 
normally think of as film noise, and listened to or watched for audience reaction. 
Watching audience reaction is a thing we do all the time in connection with pre- 
view work, so that we become reasonably conscious of the audience reaction. We 
find that audiences do not quiet down if there is a noise in a theater, especially if 
the noise is of a type that is irritating. A higher level noise of 60 cycles, or even 
120 cycles, does not seem to irritate the audience nearly as much as the higher- 
frequency noises, such as the film noise. We were quite pleased by the contrasts 
in audience reaction observed during tests on the picture Geronimo, where we ob- 
tained attention and audience quietness from fine-grain prints as contrasted with 
normal release prints. 

MR. MCNABB: The main reason I bring up the question is that in the broad- 
casting field, noise-measuring technic does not permit a higher level at 60 or 120 
cycles than it does of higher-frequency noises similar to film noise. Have you 
made any check on the subjective characteristics of noise? 

MR. GRIMWOOD: No. We have not attempted to evaluate the psychological 
effects of the noise. 

MR. McNABB : I notice that you said you used a weighted curve. 

MR. GRIMWOOD: For one set of measurements, yes. 

MR. McNABB : A weighted curve is not used, I believe, in broadcast work, be- 
cause, as I understood it at that time, the persistence of a noise, regardless of its 
frequency, is what makes it undesirable. That does not seem to agree very well 
with the facts. 

MR. RYDER: I think their problem is a little different from ours; for instance, 
the loading that we would normally apply when considering sound volumes as 
used in the theaters, is not a correct loading for home listening on the radio. The 
problem is different, and maybe there is good reason for it. 

MR. CRABTREE : What is the relation between the noise reduction you get by 
changing films and the noise increase you get from (a) the accumulation of 
scratches during the normal projection life of a film, and (b) the accumulation of 
silver sludge on the film in case you do not filter the developer. 



Aug., 1940] INVESTIGATION OF GROUND NOISE 137 

MR. GRIMWOOD: We have no data on that point. It is hard to evaluate the 
effect of an increase due to scratches and noises of that nature, which are much 
more objectionable than the steady noise from grains. This work was confined 
entirely to the grain noise. We were interested in the limits to which it can go 
and the minimum value to be expected. 

As far as developer sludge is concerned, we did find indications of the noise 
varying somewhat during the life of a developer variations of the order of one db 
or possibly two db, which may have been due to that cause. 

MR. BOYER: Have you made any correlation between the noise and the graini- 
ness of the film as contrasted with grain size? Have you used the method on 
negatives of fairly large grain size so that the graininess between films could be 
measured? 

MR. GRIMWOOD: We have not tried to correlate visual graininess data with 
noise measurement. Dr. Goetz and others, working at the California Institute 
of Technology, have done much work on graininess measurements. He reports 3 a 
definite correlation between objective and subjective measurements for materials 
covering a wide range of grain sizes. His published work does not, so far as I 
know, state whether the correlation holds for prints of a negative. 

MR. KELLOGG: Have you tested this with ultraviolet light? 

MR. GRIMWOOD: We have found no appreciable difference in ground noise of 
low-gamma negatives exposed with ultraviolet radiation as compared with tung- 
sten exposures. These tests have not, however, been sufficiently comprehensive 
to state definitely that there is no difference. No tests have been made at high 
gammas or in printing with ultraviolet light. 

MR. RYDER: Our experience indicates that the improvement available from 
ultraviolet light is much less on fine-grain film than on standard film. The whole 
field is too new for any of us to make any positive statements in this regard. 



FILTERING FACTORS OF THE MAGNETIC DRIVE* 
R. O. DREW AND E. W. KELLOGG** 



Summary. A laboratory model of a magnetic-drive film-phonograph was modi- 
fled so that speed fluctuations of large and measurable magnitude and of frequencies 
ranging from : /2 to 7 cycles could be introduced either into the sprocket rotation or 
the magnet rotation. The resulting speed variations at the drum were determined 
by means of a "wowmeter." The large ratios of flutter reduction indicated by these 
measurements show in part why the magnetic drive gives unsurpassed film motion. 

THE MAGNETIC DRIVE SYSTEM CONSIDERED AS A MECHANICAL FILTER 

The magnetic drive as used in RCA recorders and in film phono- 
graphs for re-recording has been the subject of several technical 
papers, 1 ' 2> 3 in which general statements are made in regard to its 
effectiveness as a filter, but up to the present no measurements have 
been reported which show in definite terms how much speed fluctua- 
tion occurs at the drum as the result of fluctuations of given magni- 
tude in the driving system. Several months ago, the authors under- 
took a series of measurements with this end in view, and although 
the data leave something to be desired in the way of precision, it is 
felt that their significance is not appreciably impaired thereby and 
that their interest is sufficient to warrant reporting. 

Mechanical filtering has been widely employed in machines for 
recording sound on film or reproducing the same, to provide smooth 
motion of the film at the translation point. In most such mechanical 
filters the film is carried on a rotating drum, on the shaft of which is a 
flywheel. In order that the drum may run at uniform speed, attempt 
is made to minimize all the forces which might act to accelerate or re- 
tard it. To this end, whatever means are used to transmit to the 
drum shaft the continuous torque needed to maintain its rotation are 
of a very yielding character, as, for example, soft springs or flexible 
loops of film. When this is done, if there are periodic speed fluctua- 
tions in the driving system, these flexible connections take up the 

* Presented at the 1940 Spring Meeting at Atlantic City, N. J. ; received 
May 23, 1940. 

** RCA Manufacturing Co., Camden, N. J. 

138 



FILTERING FACTORS OF MAGNETIC DRIVE 139 

resulting phase-shifts between the driving system and the uniformly 
running drum. They can not absolutely protect the drum from the 
effect of the fluctuations, but can make that effect extremely small. 
The "filtering factor" is the ratio of speed variations at the drum to 
those at the source of the disturbance. 

The "rotary stabilizer," which in principle is closely related to 
the magnetic drive, has been well analyzed by E. D. Cook. 4 In both 
systems damping of the drum shaft is provided by a viscous coupling 
to a second member which is rotating at the same or nearly the same 
speed. The viscous coupling is an oil film in one case and is electro- 
magnetic in the other. In order that the viscous coupling may pro- 
vide the desired damping, the second rotating member must not par- 
ticipate appreciably in the speed variations of the drum. In the case 
of the rotary stabilizer, the second member is a flywheel whose inertia 
prevents it from changing speed appreciably, while in the case of the 
magnetic drive the second rotating element, against which the damp- 
ing forces react (namely the magnet), is geared to the driving motor. 
This geared connection has a double effect of providing a relatively 
enormous effective mass, so that the magnet speed will be almost 
completely independent of any forces which may act upon it through 
the viscous coupling (a condition for optimum damping) but it may 
introduce certain small disturbances into the magnet speed, due to 
such imperfections as exist in the gearing. In the original paper 
describing the magnetic drive system, 1 a calculation is given on the 
basis of which it is shown that magnet speed fluctuations of consider- 
able magnitude result in such small speed changes at the drum as to 
be of no particular consequence. 

It would be a simple matter to make determinations of stiffness of 
film loops and of moments of inertia of the rotating parts, and on this 
basis to calculate the amount of speed fluctuation at the drum which 
would result from given fluctuations at the controlling sprockets. 
Some such calculations are given herein. The writers felt that an 
experimental attack would be of more general interest and perhaps 
more convincing to those who are not mathematically inclined. 

Residual Irregularities. Since in the best of machines there is some 
residual speed irregularity or flutter, it is practically necessary in 
measuring the filtering ratio that the irregularities deliberately intro- 
duced and measured shall be of exaggerated magnitude so that the 
residual imperfections in the film motion will not mask the speed 
variations which are deliberately introduced, or make it difficult to 



140 R. O. DREW AND E. W. KELLOGG tf. S. M. p. E. 

estimate their magnitude. In spite of resort to this expedient, the 
drum speed fluctuations which were of the same frequency as, and 
attributable to, the artificially introduced disturbances, were in many 
cases too small to estimate with any assurance. 

Effects of Disturbances Originating at the Drum Shaft. Distur- 
bances at the drum may originate in irregularities of motion at the 
sprockets, or in the magnet rotation, or be due to unbalance or varia- 
tions in friction at the drum shaft itself. The last-named effects, 
namely, disturbances originating at the drum shaft, are not peculiar 
to the magnetic drive. In fact, they are necessarily present in every 
film-propelling device. The magnitude of such disturbing forces is 
largely a question of mechanical perfection and of lubrication. The 
speed fluctuations which given forces will produce depend upon the 
mechanical impedance at the drum shaft. The fact that the magnets 
take the brunt of the acceleration load means that a flywheel of gener- 
ous proportions may be employed. This is the first requisite for pro- 
viding the desired high mechanical impedance to resist forces tending 
to cause speed changes. There is, however, in every type of filter 
(excepting those which do not provide synchronous operation) some 
form of elastic connection between the drum and the remainder of 
the system comprising the sprockets, gearing, and motor. The exist- 
ence of such an elastic connection means that resonance can occur at 
some frequency. For any disturbance which repeats itself at this 
resonance frequency, the mechanical impedance of the drum shaft is 
no longer a question of flywheel inertia, but primarily one of resistance 
or damping. The advantages of strong damping, which can readily 
be obtained with the magnetic drive, will be discussed later in con- 
nection with Fig. 7. 

We have not considered that there was occasion for including any 
considerable series of experiments to show the effect of drum-bearing 
disturbances. It may be assumed that in high-class machines, such as 
sound recorders, unbalance will be reduced to negligible magnitude 
and the bearings will be the best obtainable. The following calcula- 
tions will show that reasonable manufacturing care will bring the 
unbalance far within the tolerance range. 

Assuming a flywheel weighing 1 1 pounds, having a radius of gyra- 
tion of 2.8 inches and a 2-inch drum diameter, we find that 1 inch- 
ounce of unbalance will cause the speed to change by 0.085 per cent 
above and below average, or an rms fluctuation of 0.06 per cent. 
Although it is desirable to avoid a "wow" of even this small magni- 



Aug., 1940] FILTERING FACTORS OF MAGNETIC DRIVE 141 

tude, it should be borne in mind that 1 inch-ounce would be an inex- 
cusably large unbalance (corresponding for example to mounting the 
flywheel 0.005 inch eccentric), and that according to present stand- 
ards, recording machines are considered in excellent condition if 
when tested on a flutter bridge which includes all frequencies between 
about one cycle per second and 100 cycles, the rms flutter is 0.2 per 
cent or less. 

EXPERIMENTAL METHOD AND APPARATUS 

The principal work of which this paper is a report, consisted in 
introducing disturbances of measured amplitude and frequency, first 
in the sprocket rotation and then in the magnet rotation, and in 
measuring the corresponding speed fluctuations at the drum by means 




Magnet or 
Sprocket Pulley 



FIG. 1. Method of introducing speed changes. 

of a "wowmeter" which makes an oscillographic record of the instan- 
taneous speed covering a period of six seconds. The "wowmeter" has 
been described by Morgan and Kellogg. 5 A 1000-cycle record is used, 
and the "wowmeter" makes a record of the variations in frequency. 
It has a substantially linear scale from 985 to 1015 cycles. The posi- 
tion of the light-spot on the oscillograph film can be placed wherever 
desired so that the mean position of the oscillograph trace on its film 
is no indication of the average frequency. This permits a number of 
oscillograms to be shown on the same film, and their value is not im- 
paired by the fact that they do not show the absolute speed. It is, 
however, important to know that the frequency is at all times within 
the 3 per cent range. Means are provided for checking the average 
frequency before each oscillogram is made. 

The method of introducing disturbances consisted in driving both 
the sprocket and magnets by means of belts, and passing each belt 



142 



R. O. DREW AND E. W. KELLOGG [j. s. M. p. E. 



around a pair of idler pulleys which could be periodically shifted so as 
to produce a phase change between the driving and driven pulleys 
Fig. 1 shows schematically the belt and rocker arrangement. The 
machine used for the tests was one of the original models of the RCA 
magnetic drive recorder, an experimental machine which afforded 
the desired accessibility to the driving system. The drum is cut 
short and the machine was used as a reproducer, a photocell being 
located within the hollow drum. A 1000-cycle record, itself of low 
flutter content, was spliced into a loop and run through the machine. 




FIG. 2. Film-phonograph equipped for introducing disturbances. 

The film path is not exactly the same as that of present RCA re- 
corders, but the net film loop stiffness is not materially different. 
Therefore, the writers feel that the results are fairly representative. 
The movable idler rollers for introducing "wows" were mounted on a 
rocker driven through a connecting rod and crank. The crank was 
driven by a separate motor, the speed of which could be varied. The 
throw of the crank could also be changed to any of five positions. One 
of the belt idlers was rigidly mounted on the rocker, and the other 
was sprung so that it maintained a substantially constant pressure 
against the belt, to keep it tight. 

Fig. 2 is a front view of the machine, showing the main driving 
motor, the constant-speed jack-shaft and the marks on the sprocket 



Aug., 1940] FILTERING FACTORS OF MAGNETIC DRIVE 



143 



pulley, magnets and flywheel, for making stroboscopic observations. 
Fig. 3 is a rear view showing the film path and part of the rocker 
driving system. The rocker is here shown as locked in fixed position 
for making a reference or zero disturbance oscillogram. The holes 
for the five crank-pin positions are seen in the crank disk at the lower 
right. 

The inclusion of numerous belts and pulleys in the driving system is, 
of course, not ideal for flutter-free operation and may be responsible 




FIG. 3. Rear view of film-phonograph. 

for part of the residual flutter which appears in the oscillograms even 
when the rocker is stationary, and which is superimposed on the 
"wows" which result from the working of the rocker. 

In making a test, the film-phonograph was started and the fre- 
quency of the output checked; then the rocker was started and an 
oscillogram made, record being kept of the frequency of the rocker 
motion and of the crank position. The actual phase-shift at the 
sprocket pulley or at the periphery of the magnet was measured for 
each crank length, first statically and then checked by stroboscope 
when the machine was running. The two measurements checked 



144 R. O. DREW AND E. W. KELLOGG [j. s. M. P. E. 

very satisfactorily, showing that there was no appreciable belt slippage 
under any condition. Without such a check, it was hardly safe to 
assume that the magnets, whose inertia is high, would execute as 
large movements at full speed as they would when the rocker was 
moved slowly from one position to another. A rubberized endless 
woven belt supplied by the Russell Manufacturing Company was 
employed to drive the magnets. 

Fig. 4 shows a time-exposure of the stroboscopically illuminated 
marks on the magnet. On account of the small number of flashes 
per cycle of oscillation, a visual estimate of the amplitude of 
swing was difficult, but the time-exposure covering a number of 
cycles was very satisfactory, it being found possible to hold the drift 
to practically zero during the exposure. Table I shows the ampli- 
tudes of swing for each of the five crank positions. 

TABLE I 

Speed Changes in Magnet and Sprocket Caused by Motion of Rocker 
Magnet Drive 

Crank position 12345 

Observed double amplitude at periph- 
ery = 2a 0.16 0.295 0.50 0.690 0.770 
Swing in revolutions 2a/D . 0073 . 0134 . 0227 . 0314 . 035 
(Diameter = D = 7", Speed = 
214 rpm = 3.56 rps) 

Sprocket Drive 

Observed double amplitude at periph- 
ery = 2a (3" pulley) 0.080 0.15 0.230 0.315 0.430 

Corresponding movement at sprocket 

radius 0.0255 0.0478 0.0732 0.100 0.139 

Effects of Loop Size. As is well known to those who are at all 
familiar with the magnetic drive, the machines are designed so that 
the magnets supply slightly more forward torque to the drum shaft 
than is necessary to overcome friction, and thus subject the loop of 
film above the drum to a slight tension, which may range from almost 
zero to two or three ounces, depending on magnet current adjustment. 
The film as it leaves the drum is in a long free loop and exerts negli- 
gible force. In the tests wherein oscillations were put into the 
sprocket motion, the magnet current was adjusted to give three repre- 
sentative upper loops which we have designated as tight, normal, and 
slack. Fig. 5 shows the approximate shapes of these loops. In the 



Aug., 1940] FILTERING FACTORS OF MAGNETIC DRIVE 145 

tests with fluctuating magnet speed, two different average magnet 
speeds were used in order that the effect of changing magnetic coup- 
ling might be tested without at the same time altering the loop ten- 
sion. Thus high magnet current and reduced slip gave the same loop 
as higher slip and a weaker magnet. 

Fig. 6 shows the characteristic of a film loop similar to the upper 
loop in the machine on which our tests were made. It will be noted 
that stiffness increases rapidly with increased tension. This means 
that the degree of filtering of sprocket disturbances and the natural 




Sprocket Pulley Magnet 

FIG. 4. Time exposure of stroboscope mark. 

frequency of the filter system (as determined by flywheel inertia and 
film stiffness) are radically changed by film tension. Thus at one 
ounce average tension, the loop stiffness, for small changes, is seven 
ounces per inch; at two ounces it is twenty- three ounces per inch; 
and at four ounces it is 130 ounces per inch. These would give, with 
the flywheel and drum dimensions of the machine we used, natural 
frequencies of about 0.23, 0.40, and 1.0 cycle per second. Fig. 7 
shows the characteristics of a filter of the fundamental type of the mag- 
netic drive. The filtering is calculated on the basis of the analogous 
electrical circuit. Voltage corresponds to an alternating disturbing 
force, and current to the velocity of an alternating motion. In the 
case of the mechanical system both the motion and the force are con- 



146 R. O. DREW AND E. W. KELLOGG [J. S. M. p. E. 

tinuous, but pulsating in character when cyclic disturbances are pres- 
ent. The pulsating force or velocity is considered to be the resultant 
of a continuous or constant plus an alternating force or velocity, and 
in the analysis of filter characteristics, only the alternating component 
is considered. 

Since no attempt was made when the measurements were taken 
to specify with exactness what we called "normal," "slack," and 
"tight" loops, we can offer only an approximate check between the 
calculated and the measured "wows" at the drum. From the ob- 
served ratios of filtering between sprocket and drum, (where the ob- 
served amplitude at the drum was large enough to be measured with 
any assurance) and from the natural period of oscillation, it appears 




FIG. 5. Sketches of loops : light, normal, and slack. 

that "normal loop" corresponded to a loop stiffness of the order of 
eight ounces per inch, with about one ounce average tension. The 
natural frequency was about one cycle in four seconds. In the 
PR-23 recorder, which is the principal example of commercial mag- 
netic drive, the slowest running gear is the one on the sprocket shaft, 
which turns three revolutions per second. Cyclic or rhythmic dis- 
turbances of lower frequency are practically non-existent, and it is 
only to cyclic disturbances that the curves of Fig. 7 are directly ap- 
plicable. Since the lowest frequency of disturbance in practical 
applications is of the order of twelve times the natural frequency of 
the drum and flywheel, the filtering ratio for these cyclic disturbances 
in film motion at the sprocket would be very high and may be taken 
as substantially equal to the ratio of flywheel inertia-reactance to 
film-loop stiffness-reactance, or 144 to 1. Damping is scarcely a 
factor in the filtering of disturbances so far above the natural fre- 



Aug., 1940] FILTERING FACTORS OF MAGNETIC DRIVE 



147 



quency. The magnets help the filtering of these disturbances, not so 
much by the damping they introduce as by the fact that they make 
it possible by supplying driving torque, to work with loops under very 
low tension. Damping is of great importance in connection with 
transient disturbances, due, for example, to starting or to passing of 
splices. With inadequate damping, such a disturbance may start 
a train of oscillations which persists for a long time. The magnets 
also assist greatly in bringing the flywheel up to speed. 

Although there may be no definitely cyclic disturbances below 
sprocket rotation frequency, there are small random disturbances 





O 02 .04 06 .08 .10 .12 .14 .16 .18 
CHANGE IN LOOP LENGTH - INCHES 



01 23456 
OUNCES TENSION 



FIG. 6. Film loop characteristics. 

whose origin is hard to trace but which make plenty of trouble in an 
inadequately damped system. Some possible causes are variations 
in the stiffness of the film from point to point, which cause variations 
in the force transmitted through a loop, friction which does not ex- 
actly repeat its pattern from one revolution to the next, and jerks 
from the film supply or take-up systems. It is these random dis- 
turbances which have been the downfall of practically all undamped 
systems. 

Referring to Fig. 7, it will be seen that with the damping corres- 
ponding to curve /, at the highest point on the curve (/// = 0.7) the 
speed changes at the drum are 15 per cent greater than at the sprocket, 
but if the damping is only one-fifth as much as that which gave curve 



148 



R. O. DREW AND E. W. KELLOGG 



[J. S. M. p. E. 



/, the speed changes would be five times greater at the drum than 
at the sprocket, as shown in curve //. Forces which act in a ran- 
dom manner can impart energy to oscillating systems at any fre- 
quency to which these systems are sensitive. The energy imparted 
within a narrow range of frequency is small, and since the forces or 




.2 .3 .4 

FIG. 7. 



.6 B 1.0 fw//o ^ 3 4 6 8 10 

Filter characteristics. 



disturbances themselves are small in a well built machine, the harm- 
ful effect on drum motion is negligible unless the resonant proper- 
ties of the filter cause a considerable magnification of the disturbances. 
For this reason, curve / represents a performance which experience 
has shown to be very satisfactory, while curve // would result in 
chronic trouble from "wows," which will come and go in an erratic 
manner. 



Aug., 1940] FILTERING FACTORS OF MAGNETIC DRIVE 



149 




FIG. 8. Effects of driving sprocket at irregular speed. 
MEASURED DRUM SPEED FLUCTUATIONS WITH DISTURBANCES AT SPROCKET 

Fig. 8 shows a number of oscillograms, selected as representative 
of those taken. One of the traces was made with no sprocket "wows" 
introduced, and thus represents the imperfections in the film plus the 
residual disturbances in the machine used for the tests when acting as 
a reproducer or film-phonograph. The oscillograms look ragged, but 
in judging this, the sensitivity of the "wowmeter" must be considered. 
The total variation, minimum to maximum in a period of six seconds, 
is about 0.2 per cent, and if slow changes (of the order of 0.1 per cent 



150 



R. O. DREW AND E. W. KELLOGG 



[J. S. M. P. E. 



in this case) taking place over a period of several seconds are elimi- 
nated, as is very commonly done in flutter measurements, it will be 
recognized that this represents a good standard of performance in re- 
cording machines. It is sufficient, however, to make it difficult to 
estimate the flutter produced by the operation of the rocker, when 
that flutter is small, and the smaller values are thus open to con- 
siderable question. 




:R 



FIG. 9. Calculated and observed amplitudes (normal loop). 

Curves /; measured values of speed fluctuation. 

Curves //; calculated. 

Curves ///; speed fluctuations at sprocket. 



A purely objective method of measuring that portion of the total 
flutter which is of the same frequency as the rocker motion would 
have been desirable but would have required equipment which was 
not available. We therefore simply made visual estimates. Di- 
rectly under a number of the oscillograms are sinusoidal curves which 
in our estimation represent approximately the amplitude of the com- 
ponent, of the same frequency in the recorder flutter. From these 
curves, the reader may check whether the figures reported fairly rep- 



Aug., 1940] FILTERING FACTORS OF MAGNETIC DRIVE 



151 



resent the flutter resulting from the disturbances introduced by the 
rocker. A scale is shown at the end of the oscillogram. The esti- 
mated double amplitude of speed fluctuation, in per cent of 
average film speed, is marked on the curve. Although the method 
of determining the magnitude of the flutter is crude, it can certainly 
be said that the true value does not materially exceed the figure given. 
This gives a basis for stating that the filtering ratio is at least as large 
as reported. 

Fig. 9 is a series of plots on which the measured values of flutter 
amplitude are shown by the solid curves marked /. Calculated 
curves, marked //, are also drawn showing the theoretical shape of 




FIG. 10. Comparison of motion at sprocket (a) and at 
drum (6). (a, zero field current 2 w/sec., pos. 1; b, 
normal size loop, 2 w/sec., pos. 1.) 

the flutter amplitude curve, based on the assumption of a loop stiffness 
of eight ounces per inch. In making all the oscillograms, the galva- 
nometer of the "wowmeter" was shunted by a condenser, so that it 
would not record the rapid flutter due to vibration and other factors 
having nothing to do with the relatively low-frequency "wows" 
introduced by the rocker which we were attempting to measure. The 
"wowmeter" was calibrated with the condenser in place, and cor- 
rections applied for the differences in response at the several rocker 
frequencies used. The straight lines through the origins in Fig. 9 
(marked /// in each case) show the magnitude of the per cent speed 
variations at the sprocket as calculated from the rocker frequency 
and amplitude of phase-shift. These curves run off the edge of the 
diagrams and are continued at one-tenth scale in the lines marked 



152 



R. O. DREW AND E. W. KELLOGG [J. S. M. p. E. 



/// -4- 10. Fig. 10 is a pair of oscillograms made to give a direct indi- 
cation of the relative speed changes at the sprocket and at the drum. 
Curve b is made in the usual way (but with the rocker in action). 
Curve a is made with the drum locked and the film sliding over it, thus 
making it serve as a gate. The pressure-roller was lifted, but a light 
pressure-finger applied to hold the film against the drum, and to cause 
the film to be pulled tight between the reproducing point on the drum 
and the sprocket. Under these conditions the speed fluctuations at 
the scanning point are substantially the same as at the sprocket. 




FIG. 11. Speed fluctuations (slack loop). FIG. 12. (tight loop). 



Fig. 11 is a set of curves similar to those of Fig. 9, but based on 
oscillograms made with a slack loop. In practically all cases the 
flutter of rocker frequency was so small that its measurement was 
very uncertain. The actual stiffness of the slack loop is difficult to 
estimate, but is evidently so low that practically no disturbance is 
transmitted through the loop, except perhaps at the lowest rocker 
frequencies tried. 

Fig. 12 shows a similar plot based on oscillograms made with a 
tight loop. Only the smallest crank throw was used with a tight loop, 



Aug., 1940] FILTERING FACTORS OF MAGNETIC DRIVE 



153 



since otherwise the phase-shifts at the sprocket are sufficient to take 
up practically all the excess film in the loop and subject the film at 
the drum to a series of violent jerks, unlike anything that could 
happen in service. 

Fig. 13 shows the filtering ratios as derived from the data of Fig. 
9. Owing to the large range of values to be covered, a logarithmic 
scale has been used. 



DRUM-SPEED CHANGES DUE TO IRREGULARITIES IN MAGNET-SPEED 

It is a simple matter to calculate the drum-speed fluctuations pro- 
duced by magnet-speed variations, provided the coefficient of coup- 
ling and the moment of inertia are 
known. If there should be any 
magnet-speed fluctuations of fre- 
quency near the natural frequency of 
the system, then the effect of the 
film loop must be taken into ac- 
count. This is indicated by the dif- 
ference between curves IV and VII 
of Fig. 7. The effects of magnet- 
speed fluctuations may be calculated 
in the same manner as unbalance or 
friction variations. The deviations 
in magnet-speed above and below 
normal, multiplied by the coeffi- 
cient of coupling (7.5 inch-ounces 
per rev. per sec. slip, in the case of 
our test machine, with 1.05 field 
amperes, which gave "normal loop") 
give the accelerating and retarding 
torques which act on the flywheel. 
The speed changes at the drum are 
found by dividing the alternating 
torque by the mechanical impedance 
(which in most cases is simply the 
inertia reactance of the flywheel 
and drum, or 2irf w l, where f w is 
the frequency of the disturbance 

and / the moment of inertia of flywheel and drum. Well above 
resonance a very simple relationship holds; namely, that the drum- 



600 



400 



200 



100 

80 

60 

40 
30 

20 



PCS 



I 2345676 
FREQUENCY - f w 

FIG. 13. Filtering ratios for 
sprocket disturbances. 



154 



R. O. DREW AND E. W. KELLOGG 



[J. S. M. p. E. 



speed changes bear a fixed relation to the amplitude of the magnet 
phase-shifts, independently of the frequency of the disturbance. 
Thus, for example, if an eccentric gear in the magnet-driving system 
causes the magnets to be advanced and retarded by 0.001 revolution 
(0.360 degree) with each revolution of the gear, the magnet speed 
changes will be 27r/ w X (0.001) revolutions per second, the torque will 






FIG. 14. Effect of driving magnet at irregular speed. 

be K times this, where K is the coefficient of coupling, and the 
drum-speed changes will be 

0.001.K 



In our case K equaled 7.5 at 1.05 amperes, and the moment of iner- 
tia / for the 11-pound flywheel with 2.8-inch radius of gyration is 



Wr\ = 16 X 11(2.8) 2 
2 12 X 32.2 



= 3.57 oz.-in. 2 



Aug., 1940] FILTERING FACTORS OF MAGNETIC DRIVE 



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156 R. O. DREW AND E. W. KELLOGG [j. s. M. p. E. 

The drum-speed fluctuations resulting from the magnet-shift 
assumed would be (0.001 X 7.5)/3.57 = 0.0021 radians per second, 
which with a two-inch drum would cause a film-speed change of 
0.0021 inch per second, or: 0.21/18 = 0.0116 per cent speed change. 

Fig. 14 shows several oscillograms made with the magnets moved 
forward and backward by the rocker. The measured wows are 
shown in Table II. The symbol f w stands for the frequency of the 
rocker movement, M is the per cent change in magnet-speed, and D 
is the per cent change in drum-speed. All quantities are given in 
terms of double amplitude. The magnet current was 1.05 amperes. 
The ratio of M to D gives an idea of the filtering between the magnet 
and the drum. 

In a series of tests in which the magnets were shifted forward and 
backward by means of the rocker, we found that the measured 
"wow" at the drum was practically independent of film-loop tight- 
ness except as the tighter loop was obtained by slightly larger magnet 
current and therefore stronger coupling. At one-half cycle per second 
there was an increase in amplitude with the tight loop, due to the 
fact that with the tight loop the resonance of the system was not far 
removed from the excitation frequency. 

IRREGULARITIES IN SLIP-RING CONTACT RESISTANCE 

Two brushes on each slip-ring are provided in RCA machines em- 
ploying magnetic drive, but it has sometimes happened that the sur- 
face of a slip-ring became impaired and the magnet current meter 
jumped with every revolution of the magnets. There were no com- 
plaints of the resulting recordings, but naturally "jitters" of the 
meter needle were transmitted to the nerves of the operator. For- 
tunately, the film did not know about the meter needle. 

In order to measure the effect of a periodic drop in magnet current, 
we arranged a contact which was opened by a cam during about 30 
degrees of magnet rotation. Opening the contact inserted a series 
resistance and caused the current to drop momentarily. A 14-volt 
battery was used and the main adjustment rheostat set to give about 
one ampere through the magnet winding, the loop being maintained 
by further small adjustments. With the machine running, the meter 
needle fluctuated violently. Owing to the inductance in the wind- 
ing, we could not assume that the current dropped to the value deter- 
mined by resistance alone; therefore checks were made with a cath- 
ode-ray tube. Several different values of resistance were inserted by 



Aug., 1940] FILTERING FACTORS OF MAGNETIC DRIVE 



157 



the opening of the contacts. Fig. 15 shows a series of oscillograms 
taken with successively greater fluctuations. The inserted resistance 
and the minimum current, as estimated from the cathode-ray tube 
trace, is indicated on each oscillogram of Fig. 15. About 21 revolu- 
tions of the magnet are represented in the length of the oscillogram. 
It will be observed that only with the largest values of resistance does 
any pronounced disturbance appear at magnet-rotation frequency, 
and this disturbance is still scarcely more than 0.1 per cent. The 
reason that the interruption in magnet current has so little effect is 
that at no time is the magnet exerting much force on the flywheel 
(normally, the magnet torque is of the order of 1.5 inch-ounces) and 
fluctuations in this small force can not have any large effect, especially 
in view of the fact that the cycle is repeated three times per second 




FIG. 15. Effect of interrupting magnet current. 

and a force must act for an appreciable time to produce much change 
in speed. 

Obviously we do not advocate permitting slip-rings to remain in 
bad condition, but we would point out that small kicks of the meter 
needle need not be cause for alarm. 

EFFECT OF TRANSIENT DISTURBANCES 

One of the best ways of testing a mechanical filter is to touch the 
flywheel and watch the film loops. If damping is poor, the oscillation 
will persist for a number of cycles. The most important single reason 
for supplying the magnet drive on our machines is that it provides 
the indispensable damping. The damping varies somewhat from one 
machine to another, for the reason that if bearing friction is slightly 
higher in one machine than in another, a higher magnet current is 
required to give the desired loop. In general, in machines now in 



158 



R. O. DREW AND E. W. KELLOGG [J. S. M. P. E. 



the field, the damping is less than critical. In other words, if the 
flywheel is disturbed, it will swing back and forth once or twice before 
the disturbance disappears. Fig. 16 shows several oscillograms in 
which a sudden retardation was applied to the flywheel. In some 
cases the oscillograph film was slowed down to twelve seconds per 
revolution in order to make a complete record of the recovery. The 
dying out of the transient oscillation is clearly shown. These oscillo- 




Flt/J turrtnt 





FIG. 16. Effects of touching flywheel. 

grams would afford an excellent means of checking the natural fre- 
quency, except for the fact that the disturbance introduced was so 
large as to bring in the effect of non-linearity in the film-loop stiffness. 
Non-linearity causes the oscillation to be other than sinusoidal, and 
the period depends on the amplitude, somewhat as a ball, undergoing 
a series of bounces, keeps changing the period. 

In interpreting such an oscillogram of an oscillation, it must be 
borne in mind that the position of the oscillograph trace above or 
below the axis is an indication of velocity and not of displacement. 



Aug., 1940] FILTERING FACTORS OF MAGNETIC DRIVE 159 

Thus, the flywheel is forced by the applied disturbance to drop back 
in phase, and there is a period during which the speed is below nor- 
mal; but in order for the flywheel to come back to normal position, 
the speed must for a short time be above normal. In a critically 
damped system, the oscillating member, if displaced in one direction, 
comes back to normal without swinging beyond the normal position. 
The direction of motion, however, does reverse. For this reason an 
oscillogram showing velocities of movement, even if the system is 
critically damped, will show deflections below and above the axis, the 
total negative and positive areas becoming equal when the original 
phase position is reached. This point is brought up to emphasize the 
fact that slightly different impressions may be given by watching the 
film- loops in the machine from those gained by looking at the oscillo- 
gram. The difference, however, is not especially significant unless it 
comes to a question of judging whether the system is critically damped 
or not. 

From an examination of a number of oscillograms of transients 
such as shown in Fig. 16, it appears that the total time required for 
recovery after a disturbance may be shortened by working with a 
moderately tight loop. This, however, is not recommended, as the 
rapid oscillation is likely to make more aural impression, and the 
ideal way to shorten the duration of a transient is to increase the 
damping, as this causes the loop to crawl back to normal length with 
the minimum possible amount of off -speed operation. 

CHANGES IN MOTOR VOLTAGE 

The effect of a sudden change in the voltage supplied to the driving 
motor, due, for example, to the starting of some large motor on the 
system, is a matter about which the user of a recording machine will 
naturally be concerned, especially where a special power-supply for 
recorders is not provided. We arranged to produce a sudden drop of 
about 22 per cent in the voltage supplied to our driving motor. We 
could observe no effect in the oscillograms. We then observed the 
motor with a stroboscope, and the effect of the change in voltage 
was scarcely visible. Obviously, then, we could expect no effect at 
the film. The induction synchronous motors normally used to drive 
RCA recorders are heavily damped and very stiff. The stiffness with 
which a synchronous motor is locked to the supply decreases with the 
applied voltage, but the greater the inherent stiffness of the motor 
and the lighter the load, the less is the motor phase-shift. Since little 



160 R. O. DREW AND E. W. KELLOGG [j. s. M. p. E. 

power is required to drive a recorder, it is not surprising that we could 
scarcely see any effect on the motor. It is conceivable, however, that 
for certain purposes, a motor might be employed which would execute 
a considerable jump in phase when the supply voltage changes. As- 
sume as an extreme case, for example, a phase-shift of ten electrical 
degrees. The resultant shift at the sprocket would be 10/360 or 
y 3 6 of the distance that the film travels in Veo second; or Vse of 0.3 
inch, or 0.0083 inch. In view of the negligible effect at the drum of 
much larger disturbances at the sprocket, the inevitable conclusion 
is that large changes in supplied voltage will produce an imperceptible 
effect on the film motion. 

CONCLUSIONS 

The magnetic drive provides very effective filtering for disturbances 
arising at the sprocket. 

The fact that the magnets help to bring the flywheel up to speed and 
supply all the power required to overcome bearing friction, permits the 
use of a flywheel of generous size, thereby reducing the sensitivity to 
imperfections in bearing friction and balance. 

The symmetry of construction of the multipole magnet, the large 
air-gap, and the heavy copper flange permit reasonable manufacturing 
tolerances without danger of non-uniformity in the magnet drag at 
various relative positions of magnet and flywheel. This means that 
there is practically no danger of disturbances occurring at slip fre- 
quency. 

Irregularities in magnet-speed due to gearing are a conceivable 
source of disturbance in the drum-speed, but the measured attenua- 
tion between the disturbance at the magnet and at the drum is very 
large, and reasonable manufacturing tolerances make the danger of 
flutter from this source negligible. 

Damping of transients is of great practical importance, even though 
a machine with low damping may show creditable speed constancy, 
once steady-state conditions have been reached. The magnetic 
drive provides a satisfactory degree of damping. 

It is the writers' belief that the residual flutters which appear 
in practically all measurements do not signify any actual changes in 
the rate of drum rotation, but are rather matters of film shrinkage, 
contact between film and drum, and vibration . The minimizing of such 
sources of imperfect film motion depends upon refinements in con- 
struction rather than principles of design, and are not characteristic 



Aug., 1940] FILTERING FACTORS OF MAGNETIC DRIVE 161 

of any particular type of driving or filtering system. The residual dis- 
turbances indicated in our tests are within limits which are found to 
be highly satisfactory in practice, but they are enough to make it 
difficult to measure very small effects. The writers are of the opinion 
that in future designs it will be desirable to use stronger magnetic 
coupling and correspondingly reduced slip. This increases the possi- 
bility of transmitting imperfections in the magnet motion to the 
drum and therefore may call for closer tolerances in the construction 
of the magnet driving system than are necessary if the coupling is 
loose; but it will still be easily possible to make disturbances from 
this source negligible, while giving the system the benefits of quick 
starting, quick recovery from transients, and still further reducing the 
sensitivity to random disturbances which tend to produce oscillatory 
effects. 

In some filter systems damping reduces filtering. For example, 
if the damping is applied to the flexible element of the filter (analo- 
gously to putting the resistance in series with the condenser in 
Fig. 4) it reduces the ease with which the disturbances are by-passed. 
Damping the motion of the flywheel as is done in the magnetic drive 
is analogous to putting the resistance in series with the inductance, 
thereby increasing the impedance of this branch of the circuit and 
hence improving the filtering. Correspondingly, flywheel damping 
increases the mechanical impedance associated with the drum, and 
does not interfere with the free movements of the film loops as would 
a damping device which acted on the film loops. Strong damping, 
as is well shown by comparing curves 777 and VI of Fig. 7 with the 
corresponding curves 7 and IV or II and V for lower damping, makes 
film-loop adjustment less critical, in that with sufficient damping it is 
no longer so important to keep the natural frequency very low in com- 
parison with the frequency of possible disturbing forces. If critical 
damping or more is provided, there is substantial filtering even at/// w 
= 1 (instead of an exaggerated disturbance such as takes place if the 
damping is low). Flywheel damping instead of simply resisting 
changes in speed, resists all departures from normal speed, always 
pulling back when the speed is too high and exerting a forward pull 
whenever the speed is below normal. 

REFERENCES 

1 KELLOGG, E. W.: "A New Recorder for Variable-Area Recording," /. Soc. 
Mot. Pict. Eng. t XV (Nov., 1930), p. 653. 



162 R. O. DREW AND E. W. KELLOGG [J. S. M. p. E. 

2 KELLOGG, E. W. : "A Review of the Quest for Constant Speed," /. Soc. 
Mot. Pict. Eng., XXVIII (April, 1937), p. 337. 

3 KELLOGG, E. W.: U. S. Pat., Nos. 1,892,554; 1,899,571; and Re. 19,270. 

4 COOK, E. D.: "The Technical Aspects of the High-Fidelity Sound Head," 
/. Soc. Mot. Pict. Eng., XXV (Oct., 1935), p. 289. 

6 MORGAN, A. R., AND KELLOGG, E. W.: "Measurement of Speed Fluctua- 
tions in Sound Recording and Reproducing Equipment," /. Acoust. Soc. Amer., 

7 (April, 1936). 

DISCUSSION 

MR. ALBERSHEIM: The diagram that you showed seems not quite complete. 
You implied by your remarks that one can have disturbance from the sprocket 
shaft, as well as the magnets. There are really two sides to the system. You 
should show another input with another source of disturbance, and another mass 
and compliance. The total curve includes two resonant systems with one re- 
sistance combining the two. Is that not a closer approximation to the actual 
conditions? 

MR. KELLOGG : The diagram shown in Fig. 7 represents a simple system com- 
prising a mass, an elastic element, a resistance, and two sources of disturbance; 
or, more specifically, a drum and flywheel, connected through a loop of film to a 
sprocket, damping of the flywheel (by the magnet), and two sources of disturbance, 
one at the sprocket represented by E 8 and one acting at the drum E b . The 
latter may be considered as representing not only bearing friction, but also such 
torque pulsations as result from irregularities in magnet speed. The deviations 
of magnet speed above and below the average, multiplied by the coefficient of 
coupling, give the magnitudes of the torque variations tending to disturb the 
drum motion. This is explained in the paper. We have not omitted anything 
essential, although, as Mr. Albersheim suggests, a complete electrical analogue 
for the magnetic drive would include something to represent the magnet driving 
system (motor and gearing) and the magnet inertia, with a current representing 
magnet motion. Such a circuit was illustrated in a paper on "A Review of the 
Quest for Constant Speed" in the April, 1937, JOURNAL. 

With regard to the question of what filtering properties the magnet driving 
system has, we have, of course, considerable inertia in the magnets, but com- 
paratively little compliance in the gearing. I think it safe to say that such dis- 
turbance as occurs at gear-tooth frequency will be practically confined to some 
vibration, the actual changes in rotational speed being extremely small. (Purely 
vibrational magnet motion does not react on drum speed.) On the other hand, 
the lower-frequency speed changes due to eccentric gears will scarcely be filtered 
out at all from the magnet motion. Even inexcusably bad gearing, however, 
would cause only a small fraction of the magnet wow demonstrated at the Con- 
vention, and the effect of this, in turn, on the drum speed was inaudible. Hence 
we are justified in saying that with good gearing in the magnet drive the disturb- 
ance at the drum will be negligibly small. 

MR. ALBERSHEIM: The greatest difficulty in this type of drive seems to be 
the approximate synchronization of the magnet and film drum. You evidently 
want to drive the magnet a little faster than the synchronous speed, perhaps 
by 1 per cent or less. What happens if the shrinkage of the film varies? Do you 
have means for changing the speed of the magnets? 



Aug., 1940] FILTERING FACTORS OF MAGNETIC DRIVE 



163 



MR. KELLOGG : In the magnetic drive machines of present design the magnets 
run about 15 per cent faster than the drum. If, owing to shrinkage, the drum 
should run 1 per cent slower than normal, this would increase the slip, and 
therefore the magnetically supplied torque, by one part in fifteen. Of course 
in recorders the shrinkage variation is scarcely one-fourth of one per cent. We 
also use the magnetic drive in film phonographs and here the shrinkage variation 
might be as much as 1 per cent. Ordinarily, the magnet current is adjusted to 
give about the desired loop, with the particular film which is intended to be used, 
but if various films are spliced together, and no readjustment is made, the changes 
in loop tension resulting from the small differences in drum speed are far within 




FIG. 17. Electrical analogue of magnetic drive. 



Analogies: 

/i, film movement at sprocket. 
/2, film movement at drum. 
LZ, mass of magnet. 
C 2 , flexibility of film loop. 
Ei, steady pull of film. 
EI, power supply to magnet. 
D\, disturbances in sprocket drive. 
Z> 2 , variations in film stiffness, splices, 
kinks, etc. 



DZ, irregularities in drum shaft bear- 
ing friction. 

Z?4, irregularities in magnet drive gears. 

Ri, coupling between magnet and 
flange. 

RI, bearing oil viscosity. 

L 3 , mass of roller and arm. 

S, connection substituted for magnet 
drive, to make diagram applicable 
to rotary stabilizer. 



the tolerances of loop tension, which can take a range from 50 per cent to 200 
per cent of normal without measurably impairing performance. 

MR. SEELEY: I wonder if Mr. Kellogg will discuss the advantages of the mag- 
netic damping as compared with viscous or oil damping? 

MR. KELLOGG : The magnetism does not spill and does not have to be wiped up 
with a cloth. 

I suppose you would like a little more technical answer than that. There is 
no fundamental difference except the convenience of regulation. The qualities 
of the two types of damping are identical ; provided, of course, that the viscous 
damping system does not involve any actual contact. If the damping is purely 
through a film of oil, then it has identical properties with the magnetic damping. 

MR. MAURER: Is it not a fact that the magnetic damping can readily be ad- 
justed to the exact value required, whereas oil damping is subject to variations in 
temperature? 



164 R. O. DREW AND E. W. KELLOGG 

MR. KELLOGG: Quite true. We could, of course, make an oil-damped device 
that is adjustable, and the choice would then be pretty much a question of such 
considerations as weight, cost, maintenance, etc. 

MR. KELLOGG:* Since the question of a more complete diagram of the anal- 
ogous electric circuit has been brought up, it seems appropriate to reproduce 
the illustration which was printed in the April, 1937, JOURNAL. Such compliance 
or resistance as is brought in by the magnet drive gearing would be represented 
by a very small capacity, in series with a resistance, connected across at the 
point marked 5 (Fig. 17). The nature of such filtering of the magnet motion as 
this produces has been already discussed. 

The batteries Ei and EZ and the one just below D$ represent the continuous 
driving and frictional forces, but these do not enter into the filtering calculations. 

If, as a result of the disturbance Z> 4 , an alternating current I m flows through 
the inductance L-i which corresponds to the magnet mass, the resulting current 
at 7 2 (which represents drum motion irregularities) may be shown to be equal 
to I m Ri divided by the impedance of the circuit comprising RI, R 2 , L\, and C z . 
In this it is assumed that a negligible part of the current would flow around through 
the /i branch, it being part of the assumption that the resistance in that branch 
is extremely high, or, in other words, that it would take very large forces to 
appreciably alter the rate of sprocket rotation. The representation in our paper 
of the effect of magnet speed fluctuation is based on assuming a disturbing 
voltage equal to I m Ri, and simply jumps over the derivation of this relation, 
which seemed unnecessary. 

* Communicated. 



CURRENT PRACTICES IN BLOOPING SOUND-FILM* 
WM. H. OFFENHAUSER, JR. 



Summary. A review of dimensional standards fails to indicate any attempt in 
the past to standardize sound-track bloops. While it is true that there is relatively 
little difficulty due to bloops at the present time, this condition appears to be due to the 
fact that each producing organization has more or less independently arrived at some 
rule-of-thumb solution to its particular problem rather than a result of any directed 
effort on the part of the industry as a whole. 

The criteria are almost entirely empirical; the common tests are (1} peak volume 
indicator and (2} listening. This has resulted in a wide variety of bloops in use; a 
reduction in the number of sizes and types seems desirable in the interest of simplifica- 
tion. For single-track negative bloop punches this is especially important. 

The lengths of the bloop punches vary from 0.330 to 0.965 inch. A length of 0.500 
inch may be considered to represent "average" practice. There is almost complete 
agreement on the following characteristics of bloop punches; (1) The punch should be 
sharp. (2} In the case of the triangle or trapezium types, there should be rounded 
corners at the base of the triangle. 

There is no similar agreement in the use of bloops for sound positives; in the case of 
release prints, this matter is not especially pressing since release negatives are usually 
re-recorded and have few, if any, splices. 

Our films of today have a much faster tempo than the films of 1928 
and 1929; we can characterize this change in a statistical way by 
saying that our films today have a much larger number of far shorter 
scenes. This change in tempo has had a number of effects upon the 
practices in the production of films that do not appear in evidence in 
the theaters in which the films are shown. One of the practices so 
affected is blooping. 

What is a bloop? Our November, 1931, glossary, while not di- 
rectly defining a bloop, did define a blooping patch as ". . .a black 
section approximately triangular in shape introduced over a splice on a 
positive sound-track to prevent noise that the splice would otherwise 
cause during reproduction. The patch effects a gradual diminution 
of the light transmitted through the sound-track followed by gradual 
restoration to the original value. The patch may be applied with 

* Presented at the 1940 Spring Meeting at Atlantic City, N. J., as a contribu- 
tion to the work of the Standards Committee; received April 22, 1940. 

165 



166 W. H. OFFENHAUSER [j. S. M. p. E. 

black lacquer or may be a triangle of black paper or film cemented on 
the track. The same result can be accomplished by punching a tri- 
angular hole in the negative before printing." 

In the Transactions of our Society of May, 1929, appeared an 
additional part of the definition, which was deleted from the 1931 
version : "the frequency of the diaphragm movement thus caused be- 
ing below the threshold of audibility, no sound is heard." 

In the sound-head of a reproducing system a light-beam scans the 
film as the film passes by the light-beam. Since the photocell of the 
sound-head is responsive to light variations and the system reproduces 
as sound the variations in the light that occur at an audible rate, 
any variation at an audible rate other than the intended variation 
will produce undesired sound from the loud-speakers. One obvious 
source of such undesired sound is that due to the scanning of a splice 
in a film. It was in connection with the treatment of splices that the 
term blooping was first applied; in recent years, however, the term 
has been broadened in scope until it is now applied often to the treat- 
ment of practically any sort of film transmission irregularity. 

This paper will deal with the problem of blooping splices; it is 
essentially a resume of data collected by means of a questionnaire sent 
to the various producing organizations. On behalf of the Standards 
Committee of our Society, the author wishes to express his appreciation 
and thanks to the twelve major companies who cooperated in obtain- 
ing the data. As general practice in the major studios, it can be said 
that, at the present time, not a single foot of original negative film is 
found in the release negative film used to print the release prints ; all 
sound in a release print has been re-recorded. Due to the continual 
improvement in equipment and in operating skill, the amount of noise 
added in a single re-recording operation is today relatively so small 
that it is doubtful whether the difference between a print from an 
original negative and a print from a re-recorded negative could be 
observed on any except latest and newest reproducing equipments. 
Due to the fact that a large number of prints are needed for release, re- 
recording makes it possible to provide as many release negatives as 
desired with relatively equal quality in all. 

Most studios do not use a bloop punch on original negative ; this is 
especially true of variable-area. In the case of Columbia Pictures, 
who use both variable-area and variable-density, it is reported that 
they bloop-punch original variable-density negative but do not bloop- 
punch original variable-area negative. Warner Bros., on the other 



Aug., 1940] PRACTICES IN B LOOPING SOUND-FILM 167 

hand, who also use variable-density and variable-area, do notbloop- 
punch original negative. Twentieth Century-Fox reports bloop- 
punching the original dialog negative and bloop -patching the printed 
bloop on the re-recording print. 

It seems to be universal practice that a printing step occurs be- 
tween the original negative and the re-recording print. While it has 
been suggested that a direct positive by means of what may be called 
a reversed optical image (maximum slit exposure for zero modulation) 
is suitable for originals, no studio has adopted this as general practice. 

We now come to the re-recording print; here is where the greatest 
divergence in practice occurs. There are four types of print bloops in 
common use : 

(1) Printer fog bloop. 

(2) Sprayed stencil bloop. 
(5) Bloop patch. 

(4) Hand-painted bloop. 

The hand-painted bloop for the most part seems to be used where 
either a bloop of a special size is required or where a bloop of one of the 
other types did not "take." Opinion on the effectiveness of the 
various methods varies; Columbia Pictures reports that the fog bloop 
which was originally developed for use with single variable-area 
tracks, "is the only method of blooping variable-area tracks known to 
us which is completely satisfactory. All the other methods which we 
have tried fall a little short of complete satisfaction." Twentieth 
Century-Fox, on the other hand, punches dialog negative and then 
bloop-patches the re-recording print of the dialog negative, whereas 
their dubbed dialog, effects, and some music tracks are assembled us- 
ing a diagonal splice without either bloop punches or patches. Prob- 
ably the best way to summarize is to say that each studio has 
"standardized" on the method which worked out best in that particu- 
lar studio. 

In the case of release negatives, blooping is not a problem, since 
practically all studios re-record the release negative in a single piece. 
Warner Bros., for example, reports that splices occur only due to a 
recut, accidental damage to the negative during release printing or 
for censor cuts. 

Splice widths vary; in the original sound negative the reported 
widths are in the range from 0.50 to 0.85 inch. The width of the 
splice in the re-recording print is substantially the same ; where splices 



168 



W. H. OFFENHAUSER 



[J. S. M. P. E. 



occur in the release negative, they are of the same width also. In all 
these cases, most splices reported are in the direction of the smaller 
size rather than the larger. In release prints, where splices occur, the 
reported widths are larger; most of the splices being about 0.150 inch. 
Fig. 1 shows the common types of bloops in use. The earliest 
types were the triangle, used on variable-density, and the segment, 



EDGE OF FILM 



EDGE OF FILM 



CISSOID 
EDGE OF FILM 






ISOSCELES TRIANGLE 



ISOSCELES TRAPEZIUM 
MEASURED DIMENSIONS. 









WE 3 


PAR 


WE 2 


RCAI 


PI 


P2 


Ml 


M2 


WE- 16 


L 


.330" 


.355" 


.560" 


.550" 


.580" 


.740" 


.875" 


.9685" 


.355" 


t 


.257 


.271 


.250 


.243 




.235 




.2435 


.060 


H 


.085 


.088 


.1 15 


.085 


.065 


.090 


.156 


.126 


.090 


W 


.065 












.156 




.055 


D 


.300 


.315 


.308 


.285 




.280 


.305 


.306 


.105 



FIG. 1. Bloop punch data. 

used on variable-area. Chronologically, the trapezium type followed ; 
an improvement in both triangle and trapezium types was made by 
rounding the corners of the punchout holes to (1) increase the me- 
chanical strength of the film at the corners; and (2) to reduce the 
amount of dirt and lint picked up by the film. The cissoid type of 
bloop was used in connection with symmetrical variable-area tracks. 
All these bloops are for single-track films; other special bloops are 
used for push-pull. 



Aug., 1940] PRACTICES IN BLOOPING SOUND-FILM 169 

While originally the triangle and the trapezium types were used ex- 
clusively for variable-density and the segment type used for variable- 
area, today the use of a particular type of punch is not limited to a 
particular type of sound-track. 

The lengths used vary from 0.330 inch, which seems to be the short- 
est, to 0.9685 inch which is the longest regularly used. If there is an 
"average," a length of 0.500 inch may be said to represent "average" 
practice. The Goldwyn Studio uses the short dimension; Metro- 
Goldwyn-Mayer uses the long dimension; Warner Bros, uses the 
"average." A ratio of almost 3 to 1 in length is rather difficult to 
justify from purely the sound standpoint; possibly the question of 
equipment maintenance and the care with which splices are made are 
the controlling factors. It does seem possible that this ratio can be 
reduced without adversely affecting the resultant film. 

The centerline dimension is a derived dimension; it is equal to the 
dimension D minus one-half H. In measured samples, the centerline 
dimension varies from 0.235 to 0.271 inch. "Average" practice, as 
is to be expected, is represented by the 0.243-inch dimension, the 
standard location for the sound-track centerline. Inasmuch as our 
limit on sound-track centerline variation is only 0.002 inch, some ex- 
planation of the wide variation in the "derived" centerline measure- 
ment should be made. As no explanation of this variation was given 
in any of the replies to the questionnaire, the author will appreciate 
receiving whatever explanations there may be so that this material 
can be included in the Standards Committee records. For the present, 
the only assignable explanation is that it is either not considered im- 
portant or that the deviation has not been observed. 

Some quotations from the replies to the questionnaire are interest- 
ing: 

"Studios recording their originals on push-pull generally used some form of 
bloop because the push-pull cancellation was not complete. 

"The diversity of tracks and methods is so great that I doubt whether a standard 
for general use could be arrived at. On the other hand, it seems desirable that a 
standard bloop for release prints be worked out and we shall be glad to work with 
you toward this end." 

Another quotation: 

"Blooping re-recording prints is not a serious problem with class B push-pull 
re -recording as a good splice will not reproduce." 



170 W. H. OFFENHAUSER [j. s. M. p. E. 

There is one other point on which there is a degree of agreement; 
splices are not generally blooped where there is modulation ; blooping 
is done only where there is no modulation. This is particularly true if 
background effects or noise or other sound is present sufficient to mask 
the splice noise. Those who have used the diagonal splice seem to be 
in fair agreement that it is preferable where a bloop will not be used. 

It can fairly be said that at the present time there is little or no 
difficulty with bloops in the product of the major Hollywood studios. 
Each studio has more or less independently arrived at some rule-of- 
thumb solution to its particular problem; and we can say that the 
solutions are effective. At the present time the criteria are empirical ; 
listening is relied upon to a very great extent; the peak volume indi- 
cator is also used. What has "worked" in one studio, often has not 
"worked" in another. Release prints and release negatives are rela- 
tively free of splices and therefore the blooping problem remains 
within the producing studio and is not a cause for concern in distribu- 
tion. 

On behalf of the Standards Committee of our Society, the author 
will be glad to receive further comments and information on this 
subject. Especially desired are the following: 

(1} Samples of blooped films of the various types properly identified as to use. 
Acknowledgment is herewith made of the receipt of much informative material of 
this nature. 

(2} Photographs, drawings, or sketches of the apparatus and devices used to 
make the bloops. This is especially true of the fogging bloop equipment and the 
stencil-airgun equipment. A description in detail of the technic is especially de- 
sired. Please submit material suitable for publication, as we do not have on 
record descriptive material on the equipment and technics involved. 

(3) Any information concerning which equipments and technics are available 
for the free use of the industry and which are patented. 

This report has dealt with the problem as it relates to 35-mm film. 
At the present time, 16-mm practice is not sufficiently well crystallized 
to provide "average" practices. At the present time, the use of a 16- 
mm negative punch is not recommended on 16-mm sound-track 
negatives due to the physical weakening of the splice. Since the 
trapezium type of punch produces the least 16-mm splice weakening, 
it is ordinarily used where a negative punch is indicated. 

There is almost complete agreement upon several points : 

(1} The punch used should be sharp and produce a clean-cut hole. This can be 
checked under a microscope and by observing the printed bloop^d splice. 



Aug., 1940] PRACTICES IN BLOOPING SOUND-FILM 171 

(2) Most punches in use are not sharp, 
(c?) The punch should not measurably weaken the splice. 

(4} There is little or no trouble with bloops in the theater when an unspliced 
print is used. 

DISCUSSION 

MR. ROBERTS: Very often there is a double white line due to the masking 
effect of the top and bottom edges of the negative. Any cut in a film produces 
two edges due to the finite thickness of the film. These edges produce shadows, 
the separation of which depends upon the angularity of the printing beam. 
The effect is governed by the degree of collimation of the printing light. 

Mr. Offenhauser said that bloops are primarily a concern of the studio. Labora- 
tories must often use bloop punches and they are not entirely satisfactory. It 
has been our experience that most sound negative rips occur at these bloop 
punches. They break in printing machines or automatic rewinders and peel the 
film back very nicely. 

MR. HOVER: I think that the projection profession as a whole would prefer 
that there be no attempt at blooping. It would save the projectionist a lot of 
time in examining every print, especially first-run prints, which are the worst 
offenders. In the laboratories or wherever there is assembly work, the bloop- 
ing is so carelessly done that the manager of the average first-run house insists 
that his staff examine the first-run prints and check the patches. The second- 
run prints have usually had someone else check them. 

MR. RYDER: There may be reason for complaint at times, but I will say that 
the laboratory and the exchange groups are making a sincere effort, more now 
than ever before, to take care of just such difficulties. 

MR. HOVER: The worst case I have come across so far required spending 
an entire evening in inspecting a laboratory release of Gone with the Wind. 
Every part had to be recut and replaced. 

MR. CRABTREE: Do you prefer an applied bloop patch or an ink patch? Do 
the patches peel away, and, if so, what is the objection to the ink patch? 

MR. HOVER: Since my work has been largely with first-run prints, we have 
had little trouble with the applied patch. I assume that difficulty would arise 
in subsequent runs due to aging or wear. The difficulty with ink is that under 
the heat it tends to develop fine, wrinkled lines. 

MR. RYDER: There are many problems in the studio that are not obvious; 
for instance, if we are cutting from a light negative to a dark negative, we use a 
longer bloop than when we cut together two relatively well-matched negatives. 
If we have to re-splice due to recutting, we increase the length of the bloop. 

In cases where it is necessary to establish widely different print densities on 
either side of the splices, it is desirable to use a longer bloop as the short bloop 
will normally thump in reproduction. 

We are encountering additional bloop difficulty with our fine-grain film stocks; 
thus far the best answer has been to photo-bloop the prints in line with the 
procedure commonly used in conjunction with variable-area recordings. 



OPTIMUM LOAD IMPEDANCE FOR TRIODE AMPLIFIERS 
EMPLOYING FEEDBACK* 



BURTON F. MILLER** 

Summary. The apparent plate-resistance of vacuum-tubes employed in inverse 
feedback amplifier stages is shown to be a function of the degree of feedback employed. 
Equations for predicting the optimum value of amplifier load impedance for maximum 
uniistorted power output are derived, and the necessity for properly building out the 
amplifier load circuit is demonstrated. A basic circuit, employing a combination of 
two feedback elements is indicated, which permits securing the maximum undistorted 
power output from an amplifier stage while maintaining proper impedance relation- 
ships between amplifier and load circuits without the use of building-out resistors. 

The nature and degree of improvement in amplifier performance 
which may be obtained through the application of negative feedback 
has previously been described in a number of excellent papers. In 
none of these, however, does sufficient consideration appear to have 
been given to the choice of optimum load impedance for the final stage 
of such amplifiers. It is the purpose of this paper to outline briefly 
the manner in which the apparent plate resistance of the output am- 
plifier tube varies with the degree and type of feedback employed, to 
determine the optimum value of plate load impedance, and to indicate 
means of simultaneously matching the impedance of the amplifier 
plate circuit and load circuit properly. Consideration will be limited 
to those cases in which the output tube of the amplifier is operated as 
a triode. 

The manner in which the apparent plate resistance of a tube varies 
with the amount and type of feedback employed is readily demon- 
strated by consideration of the circuit of Fig. 1. In this circuit, a 
generator of alternating voltage E is inserted in the plate circuit of a 
simple amplifier in place of the normal load impedance. Two types 
of feedback have been indicated as being operative in this circuit ; the 
first of these depends upon the introduction of a fraction of the voltage 

* Presented at the 1940 Spring Meeting at Atlantic City, N. J. ; received 
April 15, 1940. 

** Warner Bros. First National Studios, Burbank, Calif. 

172 



OPTIMUM LOAD IMPEDANCE 



173 



appearing in the tube plate circuit into the tube grid circuit through 
the medium of the branch circuit r\ t r 2 and C. This type of feedback 
has occasionally been termed "constant- voltage" feedback, since it 
acts in such a manner as to tend to maintain a constant voltage across 
the load impedance in the tube plate circuit. A second source of 
feedback voltage is provided by the cathode resistor, r c . The voltage 
introduced in the amplifier grid circuit through r c acts in such a man- 
ner as to tend to maintain the current through the load circuit at a 
constant value, and for this reason feedback introduced through the 
medium of an impedance element common to both plate and grid cir- 
cuits is sometimes referred to as "constant-current" feedback. 

The reactance of the capaci- 
tance C in Fig. 1 will be as- 
sumed negligibly small com- 
pared to the sum of the resis- 
tances r\ and r 2 ', furthermore, 
the sum of these two resistances 
will be assumed high compared 
to the plate resistance of the 
tube and the value of r c . Since 
no consideration is being given 
here to the generation of dis- 
tortion in the amplifier, con- 
siderable simplicity of form is 
gained with no loss in generality by assuming the tube plate cur- 
rent to be expressed by a linear function of the grid and plate voltages. 
The equation for tube plate current is therefore written in the form 

i p = ! + * (1) 

where 

i p is the instantaneous value of plate current, 
ju is the tube amplification factor. 
e g is the instantaneous value of tube grid voltage. 
e p is the instantaneous value of tube plate voltage. 
r p is the plate resistance of the tube. 

From Fig. 1, 

e p = E r c i p (2) 

and, setting the feedback factor 




FIG. 1. Simple diagram showing feed- 
back circuits. 



174 B. F. MILLER [j. s. M. P. E. 

the minus sign being employed to conform with common usage of the 
term j8, the grid voltage becomes 

e g = -(/3E + f e t p ). (5) 

Substituting 2 and 3 in 1, and solving for i P , 



r p + r c (I + M ) 

The apparent plate resistance of the tube is defined by the ratio e P /i p , 
and from 2 and 4 this value is found to be equal to 



It should be noted that the value of apparent plate resistance of the 
tube given by equation 5 does not express the total impedance present 
in the tube plate circuit, but indicates that portion of it which may 
legitimately be associated with the amplifier tube. In the case of the 
circuit under analysis, the total resistance of the plate circuit is evi- 
dently equal to the sum of r' P and r c . 

Consideration of equation 5 reveals that if the feedback factor /3 be 
set equal to zero, thus leaving only "constant-current" feedback, the 
action of the cathode resistor tends to increase the apparent plate 
resistance of the tube above its normal value r P by an amount equal 
to juf c . On the other hand, if the cathode resistor be set equal to 
zero and be given a finite negative value, the action of the "constant- 
voltage" type of feedback has the effect of reducing the apparent 
plate resistance of the tube below its normal value by the factor 
1/(1 M/3). If both types of feedback are employed simultaneously, 
the apparent plate resistance of the tube may be equal to, greater 
than, or less than its normal value. 

In many cases it is desirable to introduce the feedback voltage &E 
at a point one or more stages of amplification ahead of the output tube 
of the amplifier. If, under such conditions, a total voltage amplifica- 
tion A exists between the point of introduction of the feedback voltage 
and the grid circuit of the output tube, it may readily be shown that 
the apparent plate resistance of the output tube is equal to 

t r p + Atr c (l + 0A) . 



Having thus briefly treated the variation of apparent tube plate 
resistance with the type and degree of feedback action employed, 
attention is now directed to consideration of the manner in which the 



Aug., 1940] 



OPTIMUM LOAD IMPEDANCE 



175 



apparent plate resistance of the tube employed in a power amplifier 
stage affects the values of those circuit components associated with 
the output circuit of such an amplifier. Numerous earlier papers 
devoted to the subject of audio-frequency amplifier design have 
pointed out that the maximum value of "power amplification" from a 
given amplifier stage is secured when the plate load impedance is 
made equal to the differential plate resistance of the tube employed. 
The expression "power amplification" as here used is taken as the 
ratio of plate circuit power output of an amplifier stage to the required 
grid circuit driving power. In general, it may readily be shown that, 
regardless of the type or degree of feedback employed, maximum 
power amplification is secured when the amplifier load impedance is 
made equal to the sum of the apparent plate resistance and the cath- 



1 '. * > 


1 


n "^ 


* 


9 . 


i. | 


i JLi 

o 


T .,, -, i 


^ ,, f 




1 



2 4- 

FIG. 2. Generalized feedback circuit. 

ode circuit resistance r c . It is not generally true, however, that the 
maximum value of undistorted power output is obtained from the 
amplifier for this condition of impedance matching. Furthermore, 
it may be assumed that in the normal recording channel, and inci- 
dently in many other amplifier services, the degree of power amplifica- 
tion obtained in a power output stage is of quite secondary importance 
when compared to the value of undistorted power which may be de- 
rived from the amplifier. 

If no restrictions are placed on the value of output impedance ex- 
hibited by the power amplifier, the optimum value of load impedance 
may be calculated in the following manner : The generalized circuit 
indicated schematically in Fig. 2 indicates an amplifier stage employ- 
ing both "constant- voltage" and "constant-current" feedback ele- 
ments. The tube plate circuit is coupled to the load resistance R, and 
a "building-out" resistance r x , through a transformer of impedance 



176 B. F. MILLER [j. s. M. P. E. 

ratio Zi:Z 2 . For the present analysis, the value of r x will be set equal 
to zero. Then the load impedance appearing in the amplifier plate 
circuit is equal to 

*L =R (7) 



A linear tube plate current characteristic as given by equation 1 
will again be assumed. For the sake of simplicity it will be further 
assumed that the cathode circuit impedance Z c is of such character 
as to present zero resistance to continuous currents, and an equivalent 
resistance r c to alternating currents. Similarly, the plate circuit load 
impedance appearing between the terminals 1 and 2 will be assumed 
to present zero resistance to continuous currents, and an effective 
resistance TL to alternating currents only. Then, if E c and Eb 
designate the grid bias and plate battery potentials, respectively, the 
continuous component of plate current is given by 



the term E c being presumed to carry its own sign of polarity. Like- 
wise, if E represents the peak a-c voltage impressed in the tube grid 
circuit, the peak value of the alternating component of plate current 
is equal to 



where the feedback factor /3 is again equal to r\/(r\ + ^2) and the 
reactance of C is neglected. 

It is now presumed that grid current flow must be avoided to pre- 
vent distortion of the grid voltage wave form, so the maximum positive 
value of the grid exciting voltage E must be limited to such a value 
that the grid never attains positive potentials with respect to the 
cathode. 

The maximum instantaneous grid voltage is equal to 

E + 0r L i Pl - r c i Pl + E c 

Setting this quantity equal to zero, the maximum permissible positive 
value of E is given by 

E(max) = (r e - 0n,)* P - EC (10} 



Aug., 1940] OPTIMUM LOAD IMPEDANCE 177 

Substituting 10 in 9 gives the maximum permissible value of alternat- 
ing plate current as 



(11) 



Thus far it has been assumed that the plate current characteristics 
of the tube employed were truly linear. This is, in any practical 
case, only approximately true over a limited range of tube plate cur- 
rent, and it is usually necessary to limit the minimum instantaneous 
value of plate current to some arbitrary value i m in order to avoid ex- 
cessive distortion due to curvature of the plate current characteristic. 
The value of i m is obviously equal to 

im = i P() i PO (ma\) (12) 

Substituting equations 8 and 11 in 12, the optimum value of the 
quantity nE c is found to be 



/*E f (opt ) = 



Substituting 13 in 11, the maximum permissible value of alternating 
plate current is given by 



(14) 



*r p -t- r c + r L 

The average power delivered by the tube to the load circuit is equal 
to 

P n = 1 *'2 rr (1ft 

c\ * Pi ' " \- L ' J I 

If the value of ipi given by 1 4 be now substituted in 15, and the 
partial derivative of P with respect to TL be taken and equated to 
zero, the solution of the resulting equation for YL leads to a value 
which insures the maximum possible power output from the amplifier. 
This optimum value of r L is, in fact, given by 

rz,(opt.) = 2r p + r c (16) 

If r c = 0, the optimum load impedance is equal to twice the value of 
the normal plate resistance of the tube, a relationship which has long 
been employed in amplifier design work. 

Equation 16 above has been derived with no general or implied 
limitations other than the assumption of a linear plate current charac- 
teristic over a limited range of values of tube plate current, the restric- 



178 B. F. MILLER [j. s. M. P. E. 

tion on grid voltage swing to such values that the grid never attains 
positive potentials with respect to the cathode, and the assumption 
that the plate current will not be permitted to drop below an arbitrary 
minimum value, i m . It is of interest to note that the optimum value 
of load impedance is quite independent of the value of feedback em- 
ployed, except in so far as " constant-current" feedback is introduced 
through the medium of r c . Since the latter factor is usually small 
compared to the value of the quantity 2r P under any normal condi- 
tions of amplifier operation it may generally be stated that the opti- 
mum load impedance is independent of the degree and type of feed- 
back employed. 

There are many conditions of amplifier operation in which the de- 
gree of impedance matching between the amplifier output circuit and 
the load circuit is of little or no consequence. On the other hand, the 
proper functioning of certain types of load circuits is predicated upon 
a condition of relatively close impedance matching between the ampli- 
fier output and the load circuits. Since the designer of an amplifier 
can seldom be fully informed regarding all the possible applications of 
a given amplifier, it is generally desirable that amplifiers be so con- 
structed as to deliver a maximum value of undistorted output power 
into a load whose impedance closely matches that of the amplifier out- 
put circuit. 

It was demonstrated in the first portion of this paper how the ap- 
parent plate resistance of a triode is dependent upon the type and 
degree of feedback employed. Reference to Fig. 2 indicates that 
when r x is equal to zero, the amplifier output impedance as measured 
at the output terminals 3 and 4 will, in the general case, be given by 
the expression 

ro = ^ (r' p + r c } (17} 

>i 

while the load impedance presented to the tube plate circuit is given 
by equation 7. Now, it is manifestly impossible to choose an output 
transformer ratio such that TL of equation 7 takes on the optimum 
value indicated by 16, while at the same time the amplifier output 
impedance r takes on the value of the load resistance R, unless both r p 
and r'p are identically equal to zero. Therefore, if a condition of im- 
pedance match is required between the amplifier output circuit and 
the load circuit, it becomes necessary to introduce an appropriate 
resistance element either in series or in parallel with the true load re- 
sistance in the amplifier output circuit. Since constant-voltage feed- 



Aug., 1940] OPTIMUM LOAD IMPEDANCE 179 

back is far more frequently employed than constant-current feedback, 
and since equation 5 indicates that when |8 is given negative values 
the apparent plate resistance tends toward lower values than the true 
plate resistance, consideration of the requirements of impedance 
matching and simultaneous maximizing of the useful amplifier power 
output will here be restricted to those cases in which r' P is equal to, 
or less than, twice the normal value of r P . Under this condition r x 
will always be required to appear in series with the true load resist- 
ance. 

If the amplifier be assumed to be delivering a total output power P 
into its load circuit, the useful power P OL delivered to the load resist- 
ance R is equal to 

T> R r 



R 



(18) 



where P Q is given by equation 15. 

Setting the impedance ratio Zi/Z 2 of the output transformer equal 
to N 2 , the load impedance appearing in the amplifier plate circuit is 
given by 

r L = (R + r x )N* (19) 

The requirement of impedance match between the amplifier output 
circuit and the load resistance is expressed by 

R = r x + r ' p + Tc (20) 

From 20, 



Substituting 21 in 18, 

7V72DD 

(22) 



- (r'p + r c ) 
Substituting 21 in 19 

r L = 2N*R - (r' v + r c ) (23) 

The maximum value of the alternating component of plate current is 
found by substituting 23 in 14, and is equal to 

Eb r v i m / n j\ 



Substituting this value of i Pl in the expression for P given by 15, and 



180 B. F. MILLER [j. s. M. P. E. 

the resulting value of P in equation 22, the following equation is ob- 
tained for the value of the useful power delivered to the load resist- 
ance R: namely 



, . 
2(r p + N*R} - r ' 

Taking the partial derivative of PQ L with respect to N 2 , and equating 
the resulting expression to zero, the optimum value for the transformer 
impedance ratio is given by 

JV 2 = 2rp ~ r ' v (26} 

2R 

Correspondingly, the optimum value of r x is given by 

(27) 



- a [i - 

\_ 



The value of r x as given by 27 is positive for all values of r' P be- 
tween the limits of zero and 2(r p r c )/3, and the values of N 2 given 
by 26 may be employed for the same range of values of r ' P . Through- 
out this range the useful power output is equal to 

Po = (E b - r p i m } 2 ^ r , < 2(r p - r e } ( ^ 

L 16(2r p r'p} ' 3 

When r' p is greater than 2(r P r c )/3, r x must be set equal to zero, 
since negative values of this resistance would imply that r x were to be 
regarded as a source of power. When r x = 0, the proper trans- 
formation ratio for an impedance match is given by 

N 2 = r ' p + Yc (29} 

R 

and the effective load resistance in the tube plate circuit is equal to 
r' P + r c . Substituting 29 in 25, the following expression for P OL is 
obtained, and is valid under all conditions when r x is equal to zero. 



3 = (r'p + r c } r E b - r p i m I 2 
L 2 ' [_2r p + r'p + 2rJ 



(30} 



This expression attains its maximum value when r' P = 2r P , as may 
readily be verified by differentiating with respect to r' P , equating the 
derivative to zero, and solving for r' P . 

From time to time commercial amplifier designs have appeared on 
the market in which a series building-out resistor was employed in 
the amplifier output circuit, even though no feedback was employed 
in the amplifier. The designers, in justification of this step, have 



Aug., 1940] OPTIMUM LOAD IMPEDANCE 181 

pointed out that greater undistorted power output could be obtained 
when such building-out resistors were employed than could be secured 
in their absence. The truth of this statement evidently hinges on the 
degree of distortion which is considered tolerable, and on the depar- 
ture of the actual tube characteristics from the simple linear charac- 
teristic assumed throughout this paper. That the use of the build- 
ing-out resistor can not be justified if the tube characteristic is linear, 
or nearly so, will be evident from the following considerations. 

In the absence of feedback, the apparent and true plate resistances 
assume identical values. The resistance r c , in the sense employed in 
this paper, must be assumed equal to zero, the necessary bias poten- 
tial for the tube being supplied by the source E c . Then, setting r' P = 
r P , and r c = 0, the maximum undistorted power output of the ampli- 
fier for r x = is given by substituting these values in equation 30, and 
is equal to 

(P?i _ Y 4 \^ 

~P \-*- J b * pvinj fo~i\ 

\\j A. j 

Now let it be assumed that a building-out resistor is employed, and 
that the impedance ratio of the output transformer is so chosen that 
the load resistance presented to the tube plate circuit is equal to 2r/>. 
Accordingly, 

N*(R + r x ) = r L = 2r p (32) 

For a condition of matched impedance between amplifier and load, 

R = + r x (33) 

Substituting the value of r x given by 33 in 32, and solving for the 
optimum transformation ratio, 

* = & w 

From 14, the maximum value of alternating plate current would be 

i Pl (max) = ^I? 

and the substitution of this value in 15 would indicate a total power 
output from the amplifier equal to 



182 



B. F. MILLER 



[J. S. M. P. E. 



Employing 33 and 34, it is found that 



(36) 



The useful power actually delivered to the load resistor R is therefore 
equal to 

P_ 3(Eb Pplm) fof7\ 

L ~ 77 (37) 



A comparison of equations 31 and 37 immediately indicates that 
the use of the building-out resistor in conjunction with an amplifier 
employing no feedback results in a lower value of useful power output 



to 

80 












x^* 


^ 


, 


- 






- .. 



















/ 
































/ 


























t- 60 

!* 
i" 






/ 




























,x 


x 










































v 


KunoN OF MAX. POWER OUTPUT 
WITH RATIO r P/r P . 
AMPLIFIER OUTPUT IMPEDAMCC 
MATCHED To LOAD. 
















i* -* 














10 
















a 


z o 































H 

FIG. 3. Variation of maximum power output with the ratio 

r' P /r P . 



than can be obtained by directly matching the impedance of the load 
circuit to that of the amplifier plate circuit. Should it be determined, 
experimentally or otherwise, that the actual undistorted power output 
is greater when the building-out resistor is employed in amplifiers 
operating without feedback, it must be concluded that factors other 
than those considered in this paper are operative. 

Turning now to consideration of amplifiers employing relatively 
high values of constant-voltage negative feedback, equation 5 indi- 
cates that the apparent tube plate resistance may be reduced to very 
low values as compared to the value of r p . Under this condition, the 
value of the building-out resistor r x , as given by 27, approaches the 
value of the load resistance R. On the other hand, if a sufficient de- 
gree of constant-current feedback be employed, either in conjunction 



Aug., 1940] OPTIMUM LOAD IMPEDANCE 183 

with or in the absence of a fixed amount of constant- voltage feedback, 
the value of the apparent tube plate resistance may be made equal to 
twice the value of the normal tube plate resistance. Under this con- 
dition, the value of r x should be made equal to zero, while the trans- 
formation ratio N 2 should be so chosen that a condition of impedance 
match exists between the amplifier output and the load circuits. The 
load impedance appearing in the tube plate circuit is then equal to the 
optimum value 2r P , and maximum power output from the tube is 
assured. Furthermore, since r x is equal to zero, all the power output 
of the amplifier is delivered to the load resistor R. This condition 
represents an optimum then, in the -sense that not only is the condition 
for maximum power output from the tube realized, but also that a 
condition of impedance match exists between amplifier and load. 
It must be assumed, of course, that r c is negligibly small compared to 
the value of 2r P . 

The manner in which the ratio of useful to theoretical maximum 
power output of an amplifier varies with the ratio r' P /2r P , under a 
condition of impedance match between the amplifier and load circuits, 
is shown graphically in Fig. 3. Data for this curve were calculated 
from equation 28 for all values of r' P ^ 2r P /3, r c being assumed 
negligibly small, and from equation 30 for all higher values of r' P . 
It is interesting to note that as the ratio r' P /2r P approaches zero, a 
maximum power loss of 3 db is incurred through the use of the build- 
ing-out resistor. Simultaneously, a high degree of stability in the 
value of the amplifier output impedance is assured, since the greater 
portion of this impedance is represented by the building-out resistor. 



A PRECISION INTEGRATING-SPHERE DENSITOMETER* 
J. G. FRAYNE AND G. R. CRANE** 

Summary. A densitometer employing an integrating sphere associated with a 
stable high-gain amplifier is described. Densities up to 3.0 are read directly on a 
multiple- scale logarithmic meter. Visual diffuse operation is attained by simulating 
average eye characteristic by inserting appropriate filters in optical path. 

Since the inception of sound recording on film it has been recog- 
nized that some form of sensitometric control of the negative and 
positive processing is necessary in order to obtain uniformly good 
results. Two instruments, the sensitometer and the densitometer, 
are employed in all sensitometric testing and control work. In the 
early stages of the sound-on-film recording art, there was much con- 
fusion due to the multiplicity of sensitometers which were then in 
use. This problem, however, appears to have been solved satisfac- 
torily by the wide adoption of the Eastman lib sensitometer 1 which 
is generally conceded to be the standard in its field. The same can 
not be said, however, for the densitometer, as a variety of densitom- 
eters is still in use, many of which involve design features which in- 
fluence the readings obtained on them. Since a great many of these 
instruments are of the visual type, considerable variation is found in 
the readings on any single instrument made by different observers. 
Recently there have been introduced in several laboratories physical 
densitometers which usually employ a photronic cell with a sensitive 
meter to measure the light transmitted through film, the meter being 
calibrated to read density. These instruments, however, are usually 
calibrated against strips which, in turn, have been measured on visual 
instruments; so that beyond eliminating the personal factor in ob- 
servation, these instruments still depend on another instrument for 
calibration which does involve the personal factor. Also, these in- 
struments are usually not reliable for densities greater than 1.5 due 
to the low cell currents. A very interesting design of photoelectric 

*Presented at the 1940 Spring Meeting at Atlantic City, N. J.; received 
April 15, 1940. 

** Electrical Research Products, Inc., Los Angeles, Calif. 

184 



INTEGRATING-SPHERE DENSITOMETER 185 

cell densitometer has been reported by Lindsay and Wolfe, 2 which 
overcomes many of the objections of the photronic cell type and which 
employs many features similar to those utilized in the present design. 

In view of the importance of accurate determination of density for 
sound-on-film recording, it was considered desirable to build the in- 
strument described in this paper to measure density of the silver de- 
posit based only on fundamental scientific considerations and capable 
of calibration by some absolute method. For ease of operation, it 
was decided to make this instrument direct reading, thereby eliminat- 
ing all balancing devices. 

Theoretical Considerations. While the problems involved in the 
experimental determination of density have been discussed by vari- 
ous authors, a brief resume of some of the fundamental points in- 
volved are reviewed here for the benefit of those who have not had 
the opportunity thoroughly to scan the literature on the subject. 
The fundamental definition of photographic density was originally 
given by Hurter and Driffield, 3 as follows: 

D = Iog 10 O = logio Fo/Fi, 

where F Q is the light-flux incident on the silver deposit and FI is the 
light-flux transmitted by the deposit, the ratio of these two being 
defined as the opacity of the deposit to the incident light. Now if 
the photographic silver deposit were a perfectly homogeneous layer, 
the measurement of its density would be a simple problem, involving 
as it does the measurement of the two quantities FQ and FI. The silver 
deposit, however, being granular in structure, scatters or diffuses the 
incident light-flux. Unless this is taken into consideration in measur- 
ing the transmitted flux, the resulting density measurement will de- 
pend on the optical constants of the measuring instrument. 

Specular and Diffuse Density. When a beam of collimated light 
falls on a silver image the light that is transmitted is scattered or 
diffused by the granular structure of the silver image. This is illus- 
trated in Fig. 1 which uses the same graphical illustration employed 
by Jones. 4 In this figure the lengths of the transmitted rays are in- 
dicative of the intensity of the distribution of the transmitted light. 
If some light-measuring device such as the hollow sphere is placed 
as in Fig. I (A), only the least scattered rays are collected, while if 
the same device is moved to the position shown in Fig. l(-B), all the 
scattered light transmitted by the film is intercepted. If the value 
of the light-flux measured at A is substituted in the Hurter and 



186 



J. G. FRAYNE AND G. R. CRANE 



[J. S. M. p. E. 



Driffield equation, the resulting value of D is known as the specular 
density of the image. On the other hand, if the flux as measured at 
B is used, the result is known as the diffuse density of the silver de- 
posit. The relation between values of diffuse and specular density 
was first investigated by Callier 5 and the ratio is generally known as 
"Callier's Coefficient." In so-called visual diffuse-reading densitom- 
eters the practice of diffusing the incident light is quite prevalent. 
In these instruments diffusion of the light is usually accomplished by 





FIG. 1. Diagram illustrating (A} specular density, (B) 
diffuse density. 

inserting a piece of opal glass between the light-source and the film 
deposit, the film emulsion being placed directly in contact with the 
smooth surface of the diffusing glass. A certain cone of transmitted 
diffuse light is collected at the entrance pupil of the particular optical 
system employed in this type of densitometer. The limitations and 
errors involved in the use of the so-called diffuse-reading densitome- 
ters have been discussed in detail by Koerner and Tuttle. 6 They 
point out that since it is impossible to obtain perfect diffusion with 
opal glass over a 180-degree angle, the insertion of the granular photo- 
graphic deposit will tend further to scatter the incident light. As 



Aug., 1940] 



INTEGRATING-SPHERE DENSITOMETER 



187 



the scattering increases with increasing density, less and less of the 
transmitted flux will enter the entrance pupil of the instrument, thus 
tending to make the readings depart from the theoretical 100 per 
cent diffuse condition and approach instead the specular condition 
described above. 

Integrating Sphere Density. The operation of the integrating 
sphere is illustrated in Fig. 2. A ray incident on a film sample, placed 
at the entrance of the sphere, is scattered by the emulsion. The 
scattered rays are reflected repeatedly at various angles from the in- 




PHOTO CELL 



FIG. 2. Illustrating diffusing action of inte- 
grating sphere. 

side wall of the sphere. This wall is coated with a highly diffuse and 
highly reflecting surface so that the complete inner surface assumes 
a uniform brightness. This brightness has been shown 7 to be di- 
rectly proportional to the total flux entering the sphere. The use of 
the baffle P shown in the figure is to prevent any direct rays from en- 
tering the photocell from the bottom of the sphere, which tends to be 
highly illuminated when no film, or films of low density, are present. 
With the deflecting plate present the surface of the sphere assumes 
uniform brightness under these conditions. The current generated 
in the photocell is proportional to the brightness of the sphere wall 
and therefore proportional to the light-flux transmitted through the 



188 



J. G. FRAYNE AND G. R. CRANE 



[J. S. M. P. E. 



film. To measure density at the sphere it is only necessary first to 
measure the current in the cell with no film at the sphere entrance 
window, and then with the film sample present. The common 
logarithm of the ratio of the first reading to the second reading of the 
cell currents will indicate the diffuse density of the silver deposit. 




FIG. 3. Optical schematic of densitometer. 

Optical Efficiency of Sphere. The efficiency of the integrating 
sphere, which is determined by the ratio of the light that reaches the 
cell to the light that enters the sphere, is rather low. This is due to 
absorption of the radiation by the relatively large surface of the 
sphere. The general problem of the efficiency of radiation enclosures 
has been studied in detail by Moon and Severance, 8 and this in- 
strument employs a method suggested by them which calls for the 
placing of the photocell within the limits of the sphere. This, inci- 
dentally, has been found to provide the easiest mounting of the cell 



Aug., 1940] 



INTEGRATING-SP HERE >ENSITOMETER 



189 



as well as meeting the requirement for providing maximum effi- 
ciency. With the arrangement of the cell shown in Fig. 3, and with a 
magnesium oxide diffusing surface on the inside of the sphere, an 
efficiency of approximately 5 per cent has been obtained. Even with 
this low efficiency it has been found possible as described later in the 
paper, by means of suitable amplification to measure densities up to 
3.0 with a high order of stability. 

Color-sensitivity. The spectral sensitivity of the photocell em- 
ployed with the integrating sphere is of importance in the measure- 



100 



60 



40 



20 



EYE CHARACTERISTIC 
CORR. FOR TUNGSTEN LIGHT 

JENA BG-I3&OG-4 FILTERS 



4000 



WAVE LENGTH A 



7000 



FIG. 4. Comparison of eye characteristic and effective overall 
. spectral sensitivity of densitometer. 



ment of densities which are not of the ordinary neutral gray type. 
For example, photographic deposits often have a definite spectral 
selectivity which may be due to a stain induced in the developing 
process or, as in the case of fine-grain films, to scattering of the 
shorter wavelengths by the granular deposit. If the readings of the 
sphere densitometer are to agree with the visual diffuse type of 
measurement, it is necessary that a suitable filter or combination of 
filters be placed in the optical path so that the resultant spectral re- 
sponse of the photocell simulates that of the eye. The curves in Fig. 
4 show the average eye characteristic and that of the G.E. FJ-401 
photocell with Jena BG-13 and OG-4 filters placed in the optical beam. 
Both curves are corrected for tungsten light at 3100K. It will be 



190 



J. G. FRAYNE AND G. R. CRANE [j. s. M. p. E. 



noted that the two curves do not coincide exactly but this represents 
the best match that could be obtained with available filters of the 
permanent colored glass type. 

Photographic Density. Because of the spectral selectivity referred 
to above, the density of a negative measured visually may differ 
widely from the actual density as seen by the positive film in the 



100 

>- 
\ 

> 80 
h- 

CO 

#60 

LU 

| 40 

bJ 

CC 

20 



7 




POSITIVE FILM 



JENA BG-3 
FILTER - 




4000 5000 

FIG. 5. Comparison of positive film and proposed 
spectral sensitivity for measurement of printing 
density; corrected for tungsten light at 3100 K. 

printing process. This is due to the fact that the positive film is 
mainly sensitive in the blue- violet end of the spectrum. If we wish 
the densitometer to measure this printing or photographic density, 
it is necessary to filter the light falling on the cell so that the response 
of the latter simulates that of the positive film. Such filtering is 
provided by incorporating a Jena BG-3 filter, which is shown in Fig. 
5, simulating quite closely that of the positive film. There has not 
been sufficient experience at this time with the use of this latter type 
of filtering to say definitely whether it should be recommended for 



Aug., 1940] INTEGRATING-SPHERE DENSITOMETER 191 

measurement of negative densities. It is probably desirable in the 
interests of standardization to retain the visual characteristic until 
such time as some other standard of spectral sensitivity has been 
adopted for densitometric measurements. 

Density Range. In order to measure effectively the range of den- 
sities in sound photographic processes, it appears necessary to be able 
to read as high as 3.0. This means a range of 1000 to 1, or 60 db, in 
input voltage to the amplifier of the densitometer. Since it is ex- 
tremely difficult to cover this range in one scale it is desirable to use 




FIG. 6. Integrating sphere densitometer. 

a multiple scale with three ranges of density ; namely, ranges of to 
1.0, 1.0 to 2.0, and 2.0 to 3.0. This may be accomplished by inserting 
in the amplifier circuit a 40-db loss for the first range, 20-db loss for 
the second range, and no loss for the highest density range. The use 
of these loss pads is obvious when one considers the energy relation- 
ships expressed in decibels and density; namely, that the db differ- 
ence of currents for two density conditions equals twenty times the 
density difference. For example, if 7 and I\ represent the current 
values in the photocell, corresponding, respectively, to the cases 
where no film is present at the aperture and where a film with a cer- 
tain density is present, then from the explanation given above of the 



192 J. G. FRAYNE AND G. R. CRANE [j. s. M. p. E. 

operation of the sphere, the density of the film strip is given by the 
equation 

D = logio (7 //i) 

Now the input to the amplifier corresponding to a photocell current 
/i compared to that for a photocell current 7 when expressed as a 
decibel difference is : 

Adb = - 20 lo glo (7o//i) 20 (D l - D ) 

Thus we see that the decibel difference is 20 times the density differ- 
ence. It follows that a maximum density reading of 1.0 at the ex- 
treme end of the first scale can also be read as 1.0 at the other end of 
the scale by simply increasing the grain of the amplifier 20 db. 

Design. As shown in Fig. 6, this instrument has been designed to 
be mounted in a table with its panel flush with the table top The 
head assembly and meter case are above the panel, located for maxi- 
mum convenience in operation and reading. A steel case houses the 
sphere, amplifier, and associated equipment. 

Optical System. The optical system is shown schematically in 
Fig. 3. The light-source is a standard lamp with a prefocus base 
which is used in several sound reproducing systems. The filament is 
operated at a relatively low temperature to insure long life, and the 
current is supplied by a saturation type of voltage regulator which 
maintains constant current over a wide range of line voltage. Ballast 
lamps are also used and in locations where the line voltage variation 
is less than 1 volt, the regulator is not required. 

The condenser lens assembly consists of a pair of plano-convex 
lenses whose mounting also contains the colored glass filters. The 
image of the lamp filament is brought to a focus on a rectangular 
glass block which is 50 X 200 mils in cross-section. The length of 
the block is chosen to eliminate completely the coil pattern of the 
filament at the exit. The cone of light falling on this block is inter- 
rupted by a synchronously driven interrupter wheel which gives a 
frequency of 600 or 720 cycles per second on a power supply of 50 or 60 
cycles respectively. The light from the glass block is reflected down- 
ward by an aluminum-coated first-surface reflecting mirror to the 
objective lens, which brings the exit face of the block to a focus at 
the film plane. This lens is a well corrected system of high aperture 
which operates at a 2 to 1 reduction and gives a sharply defined spot 
of light of 25 X 100 mils at the film plane. Any size or shape of spot 
could be used, but this value was chosen to measure conveniently one- 



Aug., 1940] 



INTEGRATING-SPHERE DENSITOMETER 



193 



half of a 100-mil push-pull track as well as being suitable for general 
sound-track or sensitometric measurements. 

The film is placed emulsion side downward in contact with the sur- 
face of the integrating sphere, which receives all the light passing 
through the film in the manner previously described. As shown in 
Fig. 3, a baffle is provided to prevent any direct light-rays from the 
film from falling directly on to the photocell element. The cell place- 
ment was likewise chosen so that the first reflection from the brightly 
illuminated lower area of the sphere does not fall directly on the 
sensitive cell surface. 



















A 


SIGN/ 
SIGN/ 


U. FREQUENCY = 600^ (50~ OPERATION) 
U_ FREQUENCY = 720^ (60^0PERATION) 






































/ 
































/ 






V 












-10 

8 














y 








\ 












z 












/ 






A 


B 


\ 












2 20 












/ 












\ 










-30 


-0 

o 
-40 

-50 










y 














\ 


















/ 
















\ 
















/ 
















y 


































\ 







































FREQUENCY IN CYCLES PER SECOND 



FIG. 7. Frequency characteristic of amplifier. 

The aperture in the sphere affords but slight clearance over the 
dimensions of the rectangular scanning beam and, due to its relatively 
high intensity, there is no effect on the reading due to external a-c 
light or daylight of ordinary intensity. In addition, the amplifier 
characteristic discriminates against power frequency components 
as shown by Fig. 7. 

The several units of the optical system are mounted in a rigid alumi- 
num alloy casting with a removable cover which is designed to pro- 
vide adequate ventilation. The motor used to drive the interrupter 
wheel has been chosen to have a long life, and a special mounting is 
provided to minimize vibration. The sphere is mounted beneath the 
panel and has suitable adjustments for vertical and lateral position- 
ing. 



194 



J. G. FRAYNE AND G. R. CRANE [J. S. M. p. E. 



Amplifier. To raise the output from the photoelectric cell to a 
convenient level for measurement, a high-gain, stable amplifier is re- 
quired. To attain the order of accuracy required, the gain of this 
amplifier must be extremely stable with respect to temperature and 
line- voltage changes over a reasonable range. In addition, the gain 
must be constant over a wide range of signal level, with the lowest 
possible noise, which includes cathode emission noise in the first stage, 
photocell hiss, and a-c pick-up. The output meter circuit must be 
such that the meter can not be damaged when a signal 40 db above 
meter full scale is applied, for example, as when a density of 3.0 is 
suddenly removed from the gate. In addition, the reading accuracy 
of the instrument must not be affected by changing any amplifier tube. 



CALIB 



1603 



FJ40I 




FIG. 8. Simplified schematic of amplifier. 



To meet these requirements with an economy of circuit elements, 
the amplifier circuit shown schematically in Fig. 8 was adopted. Due 
to the relative inefficiency of the intergrating sphere, the output from 
the photoelectric cell is approximately 60 db/0.006 watt with no 
film, or zero density, which is reduced to a level of 120 db when 
measuring a density of 3.0. Because of these low signal levels, the in- 
put circuit is designed for a high signal-to-noise ratio, and a 600 to 
720-cycle selective circuit is employed in the feedback path to dis- 
criminate against noise components. In addition, several condenser 
values have been chosen to reduce power supply hum and the higher 
components of tube and photocell noise. By these means a noise 
level of 150 db/0.006 watt or lower has been attained, which pro- 
vides an ample margin for accurate measurement of density up to 3.0. 



Aug., 1940] INTEGRATING-SPHERE DENSITOMETER 195 

The output of the photocell is picked up across a high-impedance 
coupling circuit and applied to a stage of amplification which uses a 
low-noise pentode tube for high gain and has ample cathode feed- 
back for gain stability, linearity, and high signal-to-noise ratio. As 
previously mentioned, it was decided to cover the density range in 
three scales, which amounts to a signal range of 20 db per scale. A 
key on the panel operates on a simple voltage-divider in the output 
of the first tube, as shown in Fig. 8, to increase the gain of the ampli- 
fier by 20 and 40 db relative to the 0-1 range. A push-button on the 
same voltage-divider reduces the gain by 20 db for calibration pur- 
poses. 

Two more pentode stages further amplify the signal and employ 
feedback from the plate of the second to the cathode of the first. In 
series with the resonant circuit is a variable resistance which serves 
as a gain control for adjustment of the zero density reading of the 
indicating meter, as described below under Operation. The output 
circuit to the meter is similar to that employed in certain volume 
indicators, using a twin diode rectifier and a power pentode connected 
as a triode for the output tube. The output of this tube is made com- 
pletely degenerative to increase stability. A part of the cathode 
resistance voltage drop is used to apply a threshold voltage to the 
diode. A ballast lamp is included in the heater circuit of the output 
tube to increase its stability with normal changes in supply voltage. 

The meter settings, which are dependent on amplifier gain and plate 
current of the last tube, exhibit good stability over long periods of 
time, with the exception of a slight drift during the first few minutes 
of operation. Even during this period, errors may be avoided by oc- 
casionally checking the end points of the scale. 

Meier. Since density is fundamentally a logarithmic function, any 
attempt to indicate density using linear elements will result in an 
uneven scale on the indicating device with crowding of the scale at 
the higher density values. To facilitate observation of the scale, 
therefore, it is desirable either to make an amplifier with a logarith- 
mic response or to provide a meter the deflection of which will be a 
logarithmic function of the current supplied to the meter. While 
some success has been attained in the former over a limited range, it 
is difficult to provide such a characteristic over a range of 60 db re- 
quired to cover the density range from to 3.0 and maintain sufficient 
stability for the required accuracy. Consequently, it was decided to 
have developed a special indicating meter that would approximate 



196 J. G. FRAYNE AND G. R. CRANE [j. s. M. p. E. 

the logarithmic condition referred to above. Since it had been pre- 
viously determined to cover the density range of 1.0 for each scale it 
seemed possible that a meter with specially designed pole-pieces might 
give a reasonably uniform logarithmic response over this range, which 
corresponds to a 10 to 1 range in input current. Accordingly a special 
meter having a full-scale deflection of 20 milliamperes was developed 
by the Weston Electrical Instrument Corp., and the resulting scale 
may be seen in Fig. 6. A relatively large meter was chosen which 
provides a useful and almost linear scale approximately 5 inches long. 
It is illuminated by two lamps located within the meter housing, but 
external to the meter itself. The damping of a meter of this type is 
difficult to control because of the wide variation of flux-density at 
different scale positions, but the meter period is sufficiently high that 
little inconvenience is caused by the under-damped condition which 
exists at the left hand or end of the meter scale. 

Calibration. It is desirable in a densitometer of this kind that the 
calibration be made in some absolute manner rather than be de- 
pendent on some other type of instrument which may have funda- 
mental errors inherent in its design. Accordingly it was decided to 
make a calibration of the photocell amplifier and meter combination 
utilizing the inverse-square-law technic. An interrupted light-source 
of the same type used in the densitometer was set up so that it could 
be moved back and forth on an optical bench at known distances from 
the active surface of the photocell. Distances were then chosen so 
that the light-intensity on the photocell would be altered by integral 
decibel steps. This test was made primarily to make certain that any 
non-linearity occurring in the photocell over this range would be in- 
cluded in the overall calibration. An electrical calibration using a 
routine electrical transmission test method was likewise made of the 
amplifier and meter. The calibration determined electrically cor- 
related so closely with that obtained by the inverse-square law that 
the differences were negligible. In view of these findings and because 
the electrical calibration can be made so easily and checked at any 
time where transmission measuring facilities are available it was de- 
cided to use this method exclusively for calibrating the instrument. 
The cell current is of the order of a tenth of a microampere so that 
its life should be practically indefinite. Including the errors in the in- 
strument as well as those due to non-linear response from the photo- 
cell, the maximum probable error on the 0-1 and 1-2 ranges will not 
exceed 0.01 and on the 2-3 range it will not exceed 0.02. It is believed 



Aug., 1940] 



INTEGRATING-SPHERE DENSITOMETER 



197 



that this degree of accuracy is ample since variations of greater 
magnitude may be found in present-day sensitometric practices. 

Operation. An attempt has been made to make the operation of 
this instrument as simple and rapid as possible. The power switch 
on the densitometer controls also the voltage regulator and the power 
supply to the amplifier, as shown in Fig. 9. To use the instrument, 
the end points of the scale are first adjusted. To do this, the pointer 
is first set to by means of the left-hand knob and then to the 1.0 




FIG. 9. Block schematic of densitometer and 
auxiliary equipment. 

using the right-hand knob, with the push-button depressed. To make 
a measurement, the film is placed in the gate, emulsion side down, 
and the gate moved laterally to scan the area desired. The pressure 
spring at the gate may be swung out of the way when not wanted, 
but contact must be maintained between the emulsion and the sphere 
aperture. When the density reading exceeds 1.0, the key is thrown 
to the 1-2 position and 1.0 added to the meter reading, and likewise 
to the next scale as the density exceeds 2.0. 

In an effort to facilitate the reading of sensitometer strips, guide 
plates have been provided with suitable markings for use with strips 



198 J. G. FRAYNE AND G. R. CRANE [J. s. M. P. E. 

made on the Eastman lib sensitometer or equivalent. These guide 
plates are used in connection with the block No. 11 index mark nor- 
mally present on the sensitometer strip. This insures proper measure- 
ment at a given area of each tablet and avoids further counting to re- 
turn to, or identify any tablet. In the case of printed-through strips 
or other strips which do not have the standard index mark at block 
No. 11, provision is made on the guide plate to relocate an index mark. 
This mark then replaces the standard index mark and is used in the 
same manner. While this instrument employs a film gate designed 
for 35-mm motion picture film, it may be readily replaced by a smooth 
plate for the measurement of films or plates up to 5 inches wide. 

Comparison with Other Instruments. Preliminary comparisons 
have been made with several other densitometers in general use at 
the present time. A complete survey of all types of instruments in 
present use appeared prohibitive due to the variety of existing types, 
each with somewhat different optical constants and spectral sensi- 
tivities. Consequently, comparisons were limited to a few representa- 
tive types. The visual type was represented by the Western Electric 
KS-6466 polarization type and the Eastman Kodak Capstaff-Purdy 
wedge type as read by experienced observers. Two physical densi- 
tometers were used, one being a photronic cell type and the other a 
photocell and amplifier type, both of which have been in general use 
for some time. 

It was found that for neutral gray deposits, such as are found in 
positive sensitometric strips, close agreement was found with both 
visual and physical densitometers that had been calibrated carefully 
against visual diffuse density standards. It was noted, however, that 
readings on the polarization type of instrument were somewhat higher 
on the high-density range. In the case of the brownish colored fine- 
grain negatives, considerable deviation was found in readings made 
on the visual types. This is undoubtedly due to the extreme diffi- 
culty of judging balance when the film deposit has any noticeable 
color. The ease and rapidity of operation of the sphere desitometer 
stood out in marked contrast to that of all types tested. 

Conclusion. The integrating-sphere type of densitometer de- 
scribed in this paper associated with a stabilized high-gain electrical 
amplifying system, makes it possible to read densities up to 3.0 in 
accordance with the Hurter and Driffield definition of density. The 
readings are made quickly and easily on a direct-reading rugged 
meter and may be made either in broad daylight or in a room illumi- 



Aug., 1940] INTEGRATING-SPHERE DENSITOMETER 199 

nated with ordinary a-c lamps. The personal factor is eliminated 
in the readings and the calibration is based only on fundamental 
physical laws. While the readings are made to correlate with those 
of visual diffuse standards by insertion of suitable optical niters in 
the scanning beam, any spectral sensitivity that may later be adopted 
may be secured by inserting the appropriate color filters. 

REFERENCES 

1 JONES, L. A.: "A Motion Picture Laboratory Sensitometer," /. Soc. Mot. 
Pict. Eng., XVII (Oct., 1931), p. 536. 

2 LINDSAY, W. W., AND WOLFE, W. V.: "A Wide-Range Linear-Scale Photo- 
electric Cell Densitometer," /. Soc. Mot. Pict. Eng., XXVIII (June, 1937), p. 622. 

3 HURTER, F., AND DRiFFiELD, V. C., "Photo Chemical Investigations and a 
New Method of Determination of the Sensitiveness of Photographic Plates," 
/. Soc. Chem. Ind., IX (1880), p. 455. 

4 JONES, L. A. : "Photographic Sensitometry, Part II," J. Soc. Mot. Pict. Eng., 
XVII (Nov., 1931), p. 695. 

5 CALLIER, A.: Phot. J., XLIX (1909), p. 200. 

6 KOERNER, A. M., AND TuxxLE, C. : "Experimental Determination of Photo- 
graphic Density," /. Opt. Soc. Amer., XXVII (July, 1937), p. 241. 

7 KARRER, E.: "Use of the Ulbricht Sphere in Measuring Reflection and 
Transmission Factors," J. Opt. Soc. Amer., V (May, 1921), p. 596. 

8 MOON, P., AND SEVERANCE, D. P.: "Some Tests on Radiation Mixing 
Enclosures," /. Opt. Soc. Amer., XXIX (Jan., 1939), p. 20. 

DISCUSSION 

MR. OFFENHAUSER: Many of us are not familiar with the FJ 401 photocell. 
What type of cell is it, and what are its operating limits? 

MR. ALBERSHEIM: It is a gas-filled rubidium cell. Under the operating con- 
ditions in the RA-1100 densitometer the cell characteristic is linear so that op- 
tical and electrical calibrations agree. The density limit is 3.0. 

MR. KELLOGG: Is it logical to include the type of light-source or to duplicate 
the type of light-source, as well as the eye characteristic, in estimating visual 
effects; or, similarly, if you are measuring negatives, to include the type of 
printer light as well as the film sensitivity in the densitometer? 

MR. ALBERSHEIM: Yes, the eye characteristic is somewhat affected by the 
light-source, but this factor was taken into account in the filter-factor shown in 
Fig. 4. In the case of this densitometer, the light is somewhat reddish in color, 
because we run an incandescent lamp at low temperature, so that it will last very 
long. It is easily duplicated, and we just filtered it out to approximate the eye 
characteristic with normal light. If we wanted to use one and the same printer 
light all the time, we could multiply the film characteristic with the emission 
characteristic of the printer light and use filters which simulate that characteristic. 

MR. KELLOGG: Both factors must be taken into account. 

MR. ALBERSHEIM: The more factors eliminated, the better; but we have to 
adjust ourselves to the requirements ot the industry, and at the present time 



200 J. G. FRAYNE AND G. R. CRANE 

people are used to certain densitometers and printer factors and do not like too 
many changes at one time. When they have been using this densitometer for a 
while, and gained confidence in its consistency as a densitometer, then if they 
would like to eliminate one or two of the factors and change the filter characteris- 
tics, it can easily be done. 

MR. ROBERTS: Is it always desirable to use the integrating sphere type of 
pick-up? Do you not at times want to do sensitometry as seen by the optical 
system of your reproducer? Is there any way you can shift your pick-up so 
that it receives specular light, somewhat similar to that of a reproducer? 

DR. FRAYNE:* That can be accomplished if desired. 

MR. KELLOGG: Can you give a figure for the estimated efficiency of the 
integrating sphere? 

MR. ALBERSHEIM: Five per cent, in this particular sphere. 

MR. KELLOGG: If you can still accomplish your diffusion, the larger the frac- 
tion of the total internal area you can make the photocell represent, the better 
off you are in terms of efficiency. 

MR. ALBERSHEIM: Quite true; but it also reduces the perfection of diffusion. 
This 5 per cent is a compromise, and is about the degree of efficiency deemed 
necessary for stable amplification. The level for density of 3 goes down to an 
input of 120 db (referred to 6 milliwatts). If we had a wide-band amplifier, 
that would be close to noise level ; but due to the fact that we have a narrow range 
of amplification, we still have 30 db available, with good stability. At the same 
time, these low intensities are a slight advantage from the point of view of linearity 
of the photocell. At large amplitudes the photocells are not quite linear; at 
low intensities they are perfectly linear, and the cell amplitude characteristic does 
not affect the calibration. 

MR. EVANS: What is the area of the sample which is measured? 

DR. FRAYNE:* The scanning on the commercial instrument will probably be 
of the order of 70 X 100 mils for standard work and be capable of being reduced 
to the 25 X 100 mils which is used in this instrument. 

* Communicated. 



NEW MOTION PICTURE APPARATUS 

During the Conventions of the Society, symposiums on new motion picture appara- 
tus are held, in which various manufacturers of equipment describe and demonstrate 
their new products and developments. Some of this equipment is described in the 
following pages; the remainder will be published in subsequent issues of the Journal. 

RECORDING AND REPRODUCING SQUARE WAVES* 

D. CANADY** 



In the May, 1939, issue of the JOURNAL 1 a brief description was given of special 
film recording and reproducing equipment built for the Oscillograph Laboratory, 
Department of Psychology, Oberlin College, Oberlin, Ohio. As some interest is 
being manifested in sound engineering fields in the use of square waves for circuit 
testing, it is thought that a brief description of the associated equipment used in 
connection with the film recorder and reproducers will be of interest at this time. 

Amplifiers. Prior to the installation of the film equipment, direct-coupled 
amplifiers were designed and built under the direction of J. M. Snodgrass of the 
oscillograph laboratory. The basic requirements involved were that the com- 
pleted system be capable of handling square waves and transients of steep wave- 
front. It was quite obvious that conventional transformer- or resistance-capacity- 
coupled amplifiers were not capable of amplifying complex wave-forms of this 
nature without considerable phase-shift. A successful direct-coupled amplifier 
developed by Snodgrass in 1932 was used as a basis for the present design. The 
amplifiers are (1) quite stable in operation over long periods of time; (2) noise 
level is low at high gain ; (5) power output is ample for all requirements. Rigorous 
tests have shown that the most complex wave-forms can be amplified to high 
levels without distortion or phase shift. 

Microphones. Of several microphones available, the transverse current type 
has been used in majority of cases for direct sound pick-up. 

Light Modulators. Serious consideration was given to light modulators. Three 
were available, i. e., mirror galvanometer, ribbon light- valve, and the gaseous 
discharge lamp. The latter was finally selected as being the most suitable in view 
of the requirements involved. As pictorial considerations were unnecessary, 
"toe" recording offered several advantages, the most attractive of which was that 
negative sound-track could be reproduced or re-recorded without the additional 
time and expense involved in making prints. 

* Presented at the 1940 Spring Meeting at Atlantic City, N. J. ; received 
March 21, 1940. 

** Canady Sound Appliance Co., Cleveland, Ohio. 

201 



202 NEW MOTION PICTURE APPARATUS [J. S. M. p. E. 

A developing machine built on the premises permits maintaining the processing 
within close limits, and the toe-recorded track developed to a gamma of 2.00 has 
proved very satisfactory. 

Preliminary tests made with gaseous discharge lamps available at the time in- 
dicated that before serious work could be undertaken, lamps with stable operat- 
ing characteristics would have to be produced in sufficient quantities to permit 




FIG. 1. Wave model drawn by a Morin harmonograph. 

making replacements without investigating the idiosyncrasies of each lamp. 
Experimentation produced a lamp having the desired characteristics. The 
"current-light output" curve was linear over a wide range while the "time-cur- 
rent" curve showed little change over long periods of time. Frequency response 
and light output were satisfactory and phase-shift was not perceptible in the 
audio-frequency range. 



A jl Si ' ' I I ' I ( M ' 

f\W/^j; J - 

T vy /^ v y / -if im/ ~-ryyy/ 

. ' : i 
\ v A y A v A v A y A A A v A y A v A v A y A A A A v A v A v A v A A A A A^A y A A A A A y A y A / 



FIG. 2. Oscillogram of wave model of Fig. 1 after passing through 
three-stage transformer coupled amplifier. 

Test Procedure. Before the completed system was put into service, consider- 
able time was spent in recording and reproducing complicated wave models. 
Wave models used for the tests were drawn by a Morin harmonograph, and the 
areas inked in with India ink. These were subsequently photographed on a re- 
duced scale on film approximately 75 mm wide. After processing to a high gamma, 
the films were cleared to increase contrast between opaque and transparent areas. 

The ends of the films were cemented together to form a small loop. In making 
the tests, the small film loops could be slipped onto a constant-speed drum and 
scanned similarly to the conventional methods except on a somewhat larger scale. 



Aug., 1940] 



NEW MOTION PICTURE APPARATUS 



203 



Fig. 1 shows a wave model containing one to four complete sine waves as drawn 
by a Morin harmonograph. 

Fig. 2 is an oscillogram of the wave model shown in Fig. 1 after passing through 
the high-quality three-stage transformer-coupled amplifier. The disturbance at 
A was caused by a film patch. 




FIG. 3. Oscillogram after passing through a single 1 :1 transformer 
coupled to the direct-coupled amplifier. 



PrfTCH 



\A A A A A A A A A A A A A A A'A A A A A A A A A A A A A A A A / 
vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv 



FIG. 4. Oscillogram after passing through direct-coupled amplifier. 



Fig. 3 is an oscillogram of the wave model shown in Fig. 1 after passing through 
a single high-quality 1 : 1 audio-transformer coupled to the direct-coupled ampli- 
fier. The potential here is that of the d-c amplifier plus other distortions. (Note 
the overswing.) 



204 NEW MOTION PICTURE APPARATUS [J. S. M. p. E. 

Fig. 4 is an oscillogram of the wave model shown in Fig. 1 after passing through 
a direct-coupled amplifier. Note that the sine waves closely resemble those of 
Fig. 1, while the disturbance caused by the film patch is square- topped. Compare 
the base line with Figs. 2 and 3. 

Fig. 5 is the overall characteristic of the complete system: at the top, the wave 
model input to the direct-coupled amplifier; at the bottom, the wave model after 



FIG. 5. Overall characteristic of the complete system. 



:. 

ffffftf^ 



* v *^'^ 

5v)UfcJ -PS 



jf SOD ~ 



FIG. 6. Difference between direct-coupled and transformer- 
coupled amplifier; spoken syllable po. 

going through the direct-coupled amplifier, gaseous discharge tube, PJ-22 photo- 
cell, and preamplifier. 

Figs. 6, 7, and 8 show the difference between a direct-coupled amplifier and a 
high-quality transformer-coupled amplifier. These are actual records showing 
speech syllables as amplified by each amplifier. The differences are relatively 
striking, and show the usual asymmetries encountered in a-c amplifiers as com- 
pared with d-c amplifiers. 



Aug., 1940] NEW MOTION PICTURE APPARATUS 205 

Fig. 6 is an oscillogram of the speech syllable po as spoken by a young woman, 
using, at the top, a high-quality transformer-coupled amplifier, and at the bottom, 
a direct-coupled amplifier. Note the seeming regularity introduced by the a-c 
amplifier. 



V 
' 



^ 

"Ps 



FIG. 7. Same as Fig. 6; spoken syllable po, by a diflferent person. 



^^ 



.C,/w , , , , ^ n ^ r ,., j r ."' 

i^. gfjjjf i i ^ >i '< -i st [' \ .' '.' V V ','. i iirf.)i j ,.ji ji ji * di 

riiir'f II J * * ( ; it tt |; ( . ti t , ( , |f (1 ,, , \t \ v |i v^j^vA'i^r*; 1 

i/i ^^ 



" Worn AN. 



FIG. 8. Same as Fig. 6; spoken syllable bo. 

Fig. 7 is the same as Fig. 6 except that the syllable po is spoken by a different 
young woman. This record is particularly good in showing the asymmetry of the 
peaks in the a-c amplifier. 

Fig. 8 shows the syllable bo spoken by a young woman. In this record the peaks 
of the a-c amplifier are very great. 



206 NEW MOTION PICTURE APPARATUS [J. S. M. p. E 

Conclusion. As a matter of record, the two amplifiers used in the comparison 
tests gave identical qualities as judged by the ear. However, it is apparent that 
a Fourier analysis will give distinctly different results. It would be interesting to 
compare speech syllables after the second or third "dubbing" through a-c ampli- 
fiers with the same syllables amplified by direct-coupled amplifiers. In this case, 
the ear might detect a decided difference due to the accumulative asymmetries of 
a-c amplifiers. 

Acknowledgment is made to Messrs. Brown and Snodgrass of Oberlin College 
for their cooperation in furnishing the oscillograms accompanying this paper. 

REFERENCE 

1 CANADY, D., AND WELMAN, V. A. : "A Sound-Film Phonograph," /. Soc. Mot. 
Pict. Eng., XXX (May, 1938), p. 591. 

DISCUSSION 

MR. WELMAN: This amplifier has been made available, and Mr. Canady is 
preparing to build it particularly for some universities who want specially high 
fidelity work, which the ordinary amplifier does not fulfil. It is being made in 
portable form. 

MR. KELLOGG: In the listening tests were head-phones or loud speaker used? 

MR. WELMAN: Both head-phones and loud speaker. The same microphone 
was used for both. The tests were made largely at the university, over a period of 
three years. 

MR. ALBERSHEIM: What kind of microphone was used? 

MR. WELMAN: The microphone was made by Telefunken, model EL A M46. 
This microphone was developed by Reisz and has been manufactured by various 
concerns in Europe. It is known as a "transverse current microphone" because a 
current passes transversely across the microphone and parallel to a silken dia- 
phragm. The latter forms the front wall of a receptacle filled with carbon gran- 
ules. Current traveling transversely across the microphone is modulated by the 
variation in pressure of the carbon granules caused by the vibration of the dia- 
phragm. 

The microphone has a relatively high impedance, and faithfully handles fre- 
quencies up to 10,000 cycles. It was chosen primarily because it could be con- 
nected to the grid of the input tube without the use of a coupling transformer. 
The output is higher than that of the conventional carbon-button type and the 
hiss level is considerably lower. 

MR. SEELEY: What is the upper frequency limit of resolution of the optical 
system used in recording these waves? 

MR. WELMAN: The upper frequency limit was originally set at 10,000 cycles; 
11,000 cycles has recently been recorded. It should be borne in mind that no 
printing losses are involved as the negative track is reproduced. 

In the listening tests, head-phones and loud speakers seem to be the "bottle 
neck" of the system. 



Aug., 1940] NEW MOTION PICTURE APPARATUS 207 

PROFESSIONAL 16-MM RECORDING EQUIPMENT* 

D. CANADY** 

Direct variable-density recording is rapidly gaining favor in the 16-mm field. 
This is to be expected as good 16-mm variable-density recorded track with noise 
reduction compares favorable with 35-mm track made by commercial motion 
picture producers. Hollywood technicians are overwhelmingly in favor of the 
variable-density method and there is little doubt that 16-mm film producers will 
soon adopt directly variable-density recording as standard practice. 

Professional Type 16-mm Sound-on- Film Recorder. The professional type 
16-mm film recorder described here has been designed and built to meet the re- 
quirements of the commercial producer of 16-mm films. The complete machine 
is shown in Fig. 1. Constant film-speed is assured by a rotary stabilizer of the 
dry type, which is not affected by climatic conditions. All shafts rotate on ball 
bearings. The recording-drum shaft and recording-drum pad-roller revolve on 
precision ball-bearings selected for their smooth running qualities. Provision 
has been made for lateral adjustment of guide flanges and pad-roller pressure is 
adjustable over a wide range. 

A gaseous discharge lamp is used as a light-modulator, and the output is 
focused on the film by an optical unit of high resolving power. Microscopic ex- 
amination of frequency runs 30 to 10,000 cps recorded on standard recording emul- 
sion show clean-cut striations up to 9000 cps. As no commercial 16-mm sound 
projector is capable of reproducing frequencies of this order, the recorder should 
meet all requirements of 16-mm producers for some time to come. 

Faithful recording of high audio frequencies is necessary for good sound quality. 
Careful and precise adjustment of the optical systems in 16-mm recorders is of 
the utmost importance. Because of the restricted area available on 16-mm film, 
there is a definite limit to the number of striations that can be photographed per 
second. 

Under present standards, optimal results can be achieved by using a very nar- 
row slit sharply focused on the film. While optical units can be sharply focused 
and sealed at the factory, this practice does not permit adjustments being made 
for tolerances encountered in film stock. Furthermore, a slit image sharply focused 
on film tightly wrapped around a stationary drum will not necessarily remain in 
optimal focus when the film is in motion. In film recorders using film-driven, free- 
running recording drums mounted on ball-bearings, the distance between the 
optical unit and the emulsion surface is subject to slight variation due to (1~) types 
and makes of fUm stock and (2) degree of film flexibility. Film stock varies in 
thickness according to type and manufacturer. The flex of a film loop changes 
with respect to age and moisture content of the emulsion. Fresh stock is usually 
pliable and adheres closely to the surface of the recording drum while old or driedout 
film is less resilient and has a tendency to "bulge" away from the drum. (Fig. 2.) 

*Presented at the 1940 Spring Meeting at Atlantic City, N. J.; received April 
15, 1940. 

** Canady Sound Appliance Co., Cleveland, Ohio. 



208 



NEW MOTION PICTURE APPARATUS [J. S. M. P. E. 



Because high frequencies are completely lost when the distance between the 
optical unit and emulsion surface vary slightly, the optical system of the profes- 
sional 16-mm recorder has been provided with a micrometer focusing adjustment. 
Accurately cut detents closely spaced around the periphery of the focusing ring 
make extremely accurate focusing possible. Optimal focus for any particular 
recording stock can be effected quickly by following simple directions furnished 
with each machine. External means are provided for azimuth adjustment of 
recording slit. 

Sound-track Optical Reduction Printer. The sound-track optical reduction 
printer here described has been improved by the addition of a special optical unit. 
In conventional optical reduction printers the optical system is quite critical, 
and any irregularities of speed between the two films causes distortion of sound 




FIG. 1. Professional type 16-mm sound-on-film recorder. 



quality. Modern practice requires that the reduced track be an exact duplicate 
of the 35-mm negative; that is, if the negative is of the variable-density type, the 
16-mm track will be variable-density. If the negative is variable-area, the re- 
duced track will be variable-area. 

With the new optical unit, the reduced 16-mm track will be of the variable- 
density type regardless of the type of sound-track on the 35-mm negative. No 
direct optical relation exists between 35-mm track and the reduced 16-mm track. 
Distortion caused by shrinkage of the 35-mm track is reduced to a minimum. 

While satisfactory results have been obtained using standard exciting lamps, 
the high-pressure mercury-vapor lamp will be furnished as standard equipment 
unless otherwise specified. Optical printers can be furnished with the new optical 
unit to print 35-mm to 35-mm sound-track as well as 16-mm to 16-mm. Sixteen- 
mm prints made from 16-mm sound-track negative by optical printing are de- 
cidedly more "brilliant" than those made by contact printing. This is due to less 
slippage and increased contrast brought about by projection printing. 



Aug., 1940] NEW MOTION PICTURE APPARATUS 209 

Noise-reduction Unit for Mercury-vapor High-pressure Lamps. The noise-re- 
duction unit described in the May, 1939, issue of the JOURNAL 1 has been increased 
in size to provide noise reduction to high-pressure mercury-vapor lamps now used 
as light-sources in certain recording apparatus. Electronic in operation, the 
noise-reduction unit permits high-speed operation to prevent speech clipping. 
By applying noise reduction to the mercury- vapor lamp, danger of ribbon clash 
is entirely eliminated. With certain modifications to existing recording equip- 
ment, the 85-watt high-pressure mercury lamp can be used to replace conventional 




FIG. 2. Close-up of the mechanism. 

glow-lamps. While no tests have been made to determine the amount of phase- 
shift present, test recordings as judged by the ear to indicate there is a definite 
dropping off at high frequencies. This discrimination can, of course, be overcome 
by a compensating network in the amplifier circuit. 

REFERENCE 

1 CANADY, D. R., AND WELMAN, V. A.: "New Sound Recording Equipment," 
/. Soc. Mot. Pict. Eng., XXXII (May, 1939), p. 544. 

DISCUSSION 

MR. KELLOGG: In your second illustration, the film appeared to pass from 
under the drum around another roller. I could not see whether the latter was a 
sprocket or not. 

MR. WELMAN: It is a sprocket with an aperiodic dampening filter on it. 

MR. KELLOGG : Does the printer use a similar system? 

MR. WELMAN: Yes. The optical reduction printer consists of two indepen- 
dent rotary stabilizers connected to film-driven drums. The sprockets, take-ups, 
etc., are driven by a constant-speed motor. 

MR. THOMPSON: The statement was made that the recorder is focused to the 



210 NEW MOTION PICTURE APPARATUS [J. S. M. p. E. 

difference in thickness of various types of film from time to time. If that is the 
case, then when you start recording, how do you know whether the film is the 
right thickness or not, and how do you focus for it? Would you have to focus 
the recorder for every roll of film? If that were the case, it seems to me that the 
results would be inconsistent. 

MR. WELMAN: Our experience has been that Agfa film, for instance, is not 
the same thickness as Eastman film, and a few thousandths or parts of thou- 
sandths of an inch difference in the focusing makes a great difference in the sound. 
In the work we have done each lot of film that is used has had a sample focused at 
the beginning. 

DR. CARVER: How much do you actually have to move the focusing device? 
Is it a matter of a tenth of a thousandth? 

MR. WELMAN: The optical unit moves 0.00038" per step. With the unit 
sharply focused, a variation of three steps plus or minus is noticeable when test 
frequencies of 6000 to 8000 cycles are being recorded. 

MR. OFFENHAUSER: That seems to be contrary to our experience as manu- 
facturers of 16-mm sound-recording equipment. It has been our policy and 
practice to ship out 16-mm sound-recorders with the hope that our customers 
will not touch them. It has been our experience, too, that the whole question 
seems to be tied up with the design of the mechanism and optics of the recorder. 
If the mechanism is properly designed, the extremely small variations in the thick- 
ness of the film and of the film emulsion, as we normally meet them, are de- 
cidedly minor matters. Practically speaking, for something like three years we 
have had equipment on the market, and to the best of our knowledge and belief 
there has not been a single instance where a readjustment of focus of the equip- 
ment has been required in any one of the equipments in use. 

MR. WELMAN : On the other hand, you do not know that a readjustment might 
not have done better recording. 

MR. OFFENHAUSER: We periodically check equipment brought in to us by 
customers in the average period of a year. At the end of a yearly interval, it has 
not been found either desirable or necessary to alter the focus, not even as much as 
one five-thousandth of an inch. We put in our file the original test records, and 
then compare the original test records with those made when the machine comes in 
for repair and inspection. Ordinarily, in the case of domestic equipment, that 
occurs about once a year, and the difference between the two records usually 
shows an improvement in favor of the later-made film, on account of the fact that 
there have continually been improvements in the film stocks in the interim. The 
film manufacturers have not been telling us about it, but we do find that gradual 
improvement has been occuring almost with steady regularity. If anything, we 
find an improvement in operation after equipment has been in use and such im- 
provement, of course, we obviously can not attribute to improvement in the ma- 
chine itself, but rather in the film and its processing. The variation in film thick- 
ness and emulsion thickness seems to us to be of negligible importance. 

MR. KELLOGG: I have seen some samples, particularly of 16-mm film, that 
had such a tendency to curl that even when wrapped around a small drum, they 
still assume something of a trough-shaped form, or curl up at the edges. In a bad 
case of that kind, I think it might affect the focus. What experience has any of 
you had with such films? 



Aug., 1940] NEW MOTION PICTURE APPARATUS 211 

MR. MAURER: In Mr. Canady's recorder, if I understand correctly, is a film- 
driven drum, and the film is relatively at little tension as it goes around the record- 
ing drum. In the recorder to which Mr. Offenhauser is referring, the film is 
under considerable tension as it goes around the recording drum, and the recording 
drum is a solid surface which supports the film fully at all points across the width 
of the film. In our observation, we have run across only one piece of stock that 
was as much as half a thousandth of an inch different in thickness from the stock 
regularly supplied, and that was a piece of stock of foreign manufacture. In the 
optical system as employed, a difference of a half a thousandth in the focus would 
not produce a difference of as much as one decibel in the response at six thousand 
cycles. 

MR. CANADY:* We are a little concerned over the variation of film stock 
manufactured in the United States. When recording equipment is shipped to 
foreign countries due consideration must be taken of the fact that the customer 
may be compelled to use film stock of local manufacture. Some countries will not 
permit the importation of raw stock, and in many cases the local product differs in 
thickness and width from the American product. 

Of course, it is a simple matter to furnish an optical system that would not be 
affected by variations in film thickness, but it would not have high resolving power. 
Good quality demands that the high frequencies be faithfully recorded. In the 
16-mm field this can be done by using a carefully designed optical system. Lenses 
with high resolving power require precision adjustment facilities. Such a lens is 
either in focus or it is not. There is no "zone" where a slight variation either way 
is permissible without impairing the sharpness of the image. 

With a well designed focusing device, ail optical system of high resolving power 
is easily focused for the variations among different brands of film stock, and per- 
mits the equipment to work at maximum efficiency. 

In transit, whether over several thousand miles or across town, recording equip- 
ment is often subjected to rough handling. No matter how carefully packed or 
well built, severe shocks can throw the best optical systems out of adjustment, and 
focusing facilities for the optical system will prove invaluable. 

Where optical systems are focused and sealpd at the factory, and if adjustments 
are attempted locally without proper equipment, the results may be anything but 
satisfactory. 

When equipment is sent to the factory for adjustment, the owner is deprived of 
the use of the equipment. In some instances the time lost will be at least two to 
three months. In addition to the shipping expense involved the owner would not 
be sure that the equipment was in perfect condition when it was returned. Any- 
one who has witnessed shipping cases rolling around in the hold of a ship in heavy 
seas will understand what I mean. 

From the manufacturing standpoint, optical systems focused and sealed at the 
factory are cheaper to build. Where the interests of the customer are considered, 
the additional expense involved in the manufacture of a micrometer focusing de- 
vice is a minor factor indeed. 

* Communicated. 



CURRENT LITERATURE OF INTEREST TO THE MOTION PICTURE 

ENGINEER 



The editors present for convenient reference a list of articles dealing with subjects 
cognate to motion picture engineering published in a number of selected journals. 
Photostatic copies may be obtained from the Library of Congress, Washington, D. C., 
or from the New York Public Library, New York, N. Y. Micro copies of articles 
in magazines that are available may be obtained from the Bibliofilm Service, Depart- 
ment of Agriculture, Washington, D. C. 

American Cinematographer 

21 (July, 1940), No. 7 
Surveying Major Studio Light Levels (pp. 294-296, 

334) W. STULL 

Making a 16-Mm Middleweight Camera Dolly (pp. 

310-311) H. HUNT 

Effect of Aeration on Photographic Properties of De- 
velopers, II (pp. 319-321) J. I. CRABTREE AND 

C. H. SCHWINGEL 

Putting Scene Slate into Camera (pp. 322-323) W. STULL 

Hollywood Hears Stereophonic Reproduction ... It Is 
Good (pp. 325-326) 

British Journal of Photography 

87 (June 21, 1940), No. 4181 
Progress hi Color (pp. 301-302) 

Communications 

20 (June, 1940), No. 6 
Television in Natural Color (pp. 8, 27-28) 

Educational Screen 

29 (June, 1940), No. 6 

Motion Pictures Not for Theaters, Pt. 18 (pp. 235- 
238, 242) A. E. KROWS 

Electronics and Television and Short- Wave World 

13 (June, 1940), No. 148 
Volume Range of Sound-on-Film Recording (pp. 245- 

249) R. H. CRICKS 

Recent Progress in Television Studio Technique (pp. 

275-276, 288-289) 
212 



CURRENT LITERATURE 



213 



Institute of Radio Engineers 

28 (May, 1940), No. 5 

A System of Large-Screen Television Reception Based on 
Certain Electron Phenomena in Crystals (pp. 203- 
212) 

International Photographer 

12 (July, 1940), No. 6 
Theory of Three-Color Photography, Pt. II (pp. 7-12) 

Kinotechnik 

22 (April, 1940), No. 4 

Ueberblick iiber den Stand des Problems: Vergleich 
zwischen Zacken-und Sprossenschrift (Glance at the 
Present Position of the Problem: Comparison be- 
tween Variable Width and Variable Density) (pp. 
45-51) 

Die Anforderungen an einen zuverlassigen Belichtungs- 
messer (Requirements for an Accurate Exposure 
meter) (pp. 51-54) 

Verwendungsmoglichkeiten von Altfilm aus Azetylzellu- 
lose (Possibilities for Using Old Cellulose Acetate 
Film) (pp. 54-55) 

Motion Picture Herald 

139 (June 29, 1940), No. 13 
Hollywood Considers 3-Dimensional Sound (p. 18) 

Motion Picture Herald (Better Theaters Section) 

139 (June 29, 1940), No. 13 
Taking Advantage of the Advancement in Accessories 

(pp. 31-32, 34) 
Simplification and Convenience Mark Design of New 

Projector (pp. 34-35) 

The A. C. Arc as a Source of White Projection Light 
(p. 36) 

Photographische Industrie 

38 (May 22, 1940), No. 21 

Das Petzval-Voigtlander-Objektiv und seine Fortent- 
wicklung als Projektions-System. Ill (Further 
Development of the Petzval-Voigtlander Lens in the 
Projection System) (pp. 324-326) 

Physical Society Proceedings 

Sound-Absorbing Properties of Some Common Out- 
Door Materials (pp. 371-379) 



A. H. ROSENTHAL 



K. MARCUS 



M. ULNER 



E. RUST 



E. RADLOFF 



J. J. SEFING 



K. PRITSCHOW 



G. W. C. KAYE AND 
E. J. EVANS 



1940 FALL CONVENTION 



SOCIETY OF MOTION PICTURE ENGINEERS 



HOLLYWOOD ROOSEVELT HOTEL 

HOLLYWOOD, CALIFORNIA 
OCTOBER 21st-25th, INCLUSIVE 



Officers and Committees in Charge 

E. A. WILLIFORD, President 

N. LEVINSON, Executive Vice- President 

W. C. KUNZMANN, Convention Vice-P resident, 

J. I. CRABTREE, Editorial Vice-P resident 

L. L. RYDER, Chairman, Pacific Coast Section 

H. G. TASKER, Chairman, Local Arrangements Committee 

Pacific Coast Papers Committee 

C. R. SAWYER, Chairman 

L. A. AICHOLTZ C. FAULKNER W. A. MUELLER 

O. O. CECCARIMI C. N. BATSEL J. STEWART 

F. M. FALGE H. G. TASKER 



Reception and Local Arrangements 



N. LEVINSON 
K. F. MORGAN 
P. MOLE 

A. M. GUNDELFINGER 

H. W. REMERSCHIED 
G. S. MITCHELL 
L. D. GRIGNON 



H. G. TASKER, Chairman 
G. F. RACKETT E. HUSE 

H. W. MOYSE J. O. AALBERG 

W. C. MILLER 
W. A. MUELLER 
C. L. LOOTENS 
W. V. WOLFE 
E. C. RICHARDSON 



R. H. McCULLOUGH 
J. M. NlCKOLAUS 

E. H. HANSEN 

R. G. LlNDERMAN 

F. M. FALGE 



Registration and Information 



W. C. KUNZMANN, Chairman 
C. W. HANDLEY J. FRANK, JR. 

S. HARRIS W. R. GREENE 



214 



H. T. KALMUS 
E. HUSE 
L. L. RYDER 
C. DUNNING 

R. G. LlNDERMAN 



FALL CONVENTION 
Banquet and Dance 

N. LEVINSON, Chairman 
G. S. MITCHELL 
P. MOLE 
H. G. TASKER 
W. C. MILLER 

R. H. McCULLOUGH 



215 



G. F. RACKETT 
J. O. AALBERG 
K. F. MORGAN 
H. W. MOYSE 

J. L. COURCIER 



Hotel and Transportation 



W. C. HARCUS 
F. L. EICH 
E. M. HONAN 
H. R. LUBCKE 
W. E. THEISEN 



G. A. CHAMBERS, Chairman 

L. M. HOFFMAN 

S. P. SOLOW 

D. P. LOYE 

D. J. BLOOMBERG 

F. J. DURST 



K. B. LAMBERT 
F. O'GRADY 
A. C. BLANEY 
D. B. BROWN 
J. G. FRAYNE 



J. O. AALBERG 
C. W. HANDLEY 
W. F. RUDOLPH 

J. M. NlCKOLAUS 
J. K. HlLLIARD 



Convention Projection 

H. GRIFFIN, Chairman 
H. A. STARKE 
L. E. CLARK 
M. S. LESHING 
A. F. EDOUART 
I. SERRURIER 



J. DURST 

R. H. MCCULLOUGH 
H. W. REMERSCHIED 
H. I. REISKIND 
W. W. LINDSAY, JR. 



Officers and Members of Los Angeles Projectionists Local No. 150 



Ladies' Reception Committee 



MRS. L. L. RYDER, Hostess 
assisted by 



MRS. H. G. TASKER MRS. N. LEVINSON 
MRS. E. C. RICHARDSON MRS. P. MOLE 
MRS. G. F. RACKETT 
MRS. H. W. MOYSE 
MRS. L. E. CLARK 
MRS. G. S. MITCHELL 



MRS. C. W. HANDLEY 
MRS. K. F. MORGAN 
MRS. W. C. MILLER 
MRS. B. KREUZER 



MRS. E. HUSE 
MRS. G. A. CHAMBERS 
MRS. J. O. AALBERG 
MRS. R. H. MCCULLOUGH 
MRS. C. DUNNING 
MRS. F. J. DURST 



MRS. A. M. GUNDELFINGER 



Miss Ruth Williams, Social Director, Hollywood Roosevelt Hotel 



L. A. AICHOLTZ 
W. A. MUELLER 



Publicity 

J. HABER, Chairman 
W. R. GREENE 
G. CHAMBERS 



S. HARRIS 

A. M. GUNDELFINGER 



216 FALL CONVENTION [j. s. M. p. E. 

New Equipment Exhibit 

B. KREUZER, Chairman 

P. MOLE F. J. DURST J. G. FRAYNE 

C. N. BATSEL O. F. NEU H. W. REMERSCHIED 

K. F. MORGAN F. M. FALGE C. R. DAILY 

P. F. HARPER G. H. WORRALL C. W. HANDLEY 

Headquarters 

Headquarters of the Convention will be the Hollywood Roosevelt Hotel, where 
excellent accommodations are assured. A reception suite will be provided for the 
Ladies' Committee, and an excellent program of entertainment will be arranged 
for the ladies who attend the Convention. 

Daily hotel rates to SMPE delegates will be as follows (European Plan) : 

One person, room and bath $ 3 . 50 

Two persons, double bed and bath 5.00 

Two persons, twin beds and bath 6 . 00 

Parlor suite and bath, 1 person 8.00-14.00 

Parlor suite and bath, 2 persons 12 . 00-16 . 00 

Room reservation cards will be mailed to the membership early in September, 
and should be returned to the Hotel immediately to be assured of satisfactory 
accommodations. 

Indoor and outdoor garage facilities adjacent to the Hotel will be available to 
those who motor to the Convention. 

Members and guests of the Society will be expected to register immediately upon 
arriving at the Hotel. Convention badges and identification cards will be sup- 
plied which will be required for admittance to the various sessions, studios, and 
several Hollywood motion picture theaters. 

Railroad Fares 

The following table lists the railroad fares and Pullman charges: 

Railroad Fare Pullman 

City (round trip) (one way) 

Washington $132 . 20 $22 . 35 

Chicago 90.30 16.55 

Boston 135.00 23.65 

Detroit 106.75 19.20 

New York 135 .00 22 . 85 

Rochester 124 .05 20 . 50 

Cleveland 111.00 19.20 

Philadelphia 135 .00 22 . 35 

Pittsburgh 117.40 19.70 

The railroad fares given above are for round trips. Arrangements may be 
made with the railroads to take different routes going and coming, if so desired, 



Aug. 1940] FALL CONVENTION 217 

but once the choice is made it must be adhered to, as changes in the itinerary may 
be effected only with considerable difficulty and formality. Delegates should 
consult their local passenger agents as to schedules, rates, and stop-over privileges. 

Technical Sessions 

The Hollywood meeting always offers our membership an opportunity to be- 
come better acquainted with the studio technicians and production problems. 
Technical sessions will be held in the Blossom Room of the Hotel. Several eve- 
ning meetings will be arranged to permit attendance and participation by those 
whose work will not permit them to be free at other times. The Local Papers 
Committee is collaborating closely with the General Papers Committee in arrang- 
ing the details of the program. 

Studio Visits 

The Local Arrangements Committee is planning visits to several studios during 
the Convention week. Details will be announced in the next issue of the JOURNAL. 
Admittance to the studios will be by registration card or Convention badge only. 

New Equipment Exhibit 

An exhibit of newly developed motion picture equipment will be held in the 
Bombay and Singapore Rooms of the Hotel, on the mezzanine. Those who wish 
to enter their equipment in this exhibit should communicate as early as possible 
with the General Office of the Society at the Hotel Pennsylvania, New York, N. Y. 

Semi- Annual Banquet and Dance 

The Semi-Annual Banquet of the Society will be held at the Hotel on Wednes- 
day, October 23rd, in the Blossom Room. A feature of the evening will be the 
annual presentations of the SMPE Progress Medal and the SMPE Journal Award. 
Officers-elect for 1941 will be announced and introduced, and brief addresses will 
be delivered by prominent members of the motion picture industry. The eve- 
ning will conclude with entertainment and dancing. 

The Informal Get -Together Luncheon will be held in the Florentine Room of 
the Hotel on Monday, October 21st, at 12:30 p. M. 

Motion Pictures 

At the time of registering, passes will be issued to the delegates to the Conven- 
tion, admitting them to the following motion picture theaters in Hollywood, by 
courtesy of the companies named: Grauman's Chinese and Egyptian Theaters 
(Fox West Coast Theaters Corp.), Warner's Hollywood Theater (Warner Brothers 
Theaters, Inc.), Pantages Hollywood Theater (Rodney Pantages, Inc.). These 
passes will be valid for the duration of the Convention. 

Ladies' Program 

An especially attractive program for the ladies attending the Convention is 
being arranged by Mrs. L. L. Ryder, hostess, and the Ladies' Committee. A suite 



218 FALL CONVENTION 

will be provided in the Hotel, where the ladies will register and meet for the 
various events upon their program. Further details will be published in a suc- 
ceeding issue of the JOURNAL. 

Points of Interest 

En route: Boulder Dam, Las Vegas, Nevada; and the various National Parks. 

Hollywood and vicinity: Beautiful Catalina Island; Zeiss Planetarium; Mt. 
Wilson Observatory; Lookout Point, on Lookout Mountain; Huntington Library 
and Art Gallery (by appointment only) ; Palm Springs, Calif. ; Beaches at Ocean 
Park and Venice, Calif.; famous old Spanish missions; Los Angeles Museum 
(housing the SMPE motion picture exhibit); Mexican village and street, Los 
Angeles. 

In addition, numerous interesting side trips may be made to various points 
throughout the West, both by railroad and bus. Among the bus trips available 
are those to Santa Barbara, Death Valley, Agua Caliente, Laguna, Pasadena, and 
Palm Springs, and special tours may be made throughout the Hollywood area, 
visiting the motion picture and radio studios. 

Those who wish to visit San Francisco may arrange for stop-over privileges 
when purchasing their railroad tickets. Arrangements have been made with the 
Hotel Mark Hopkins for single accommodations for $5 daily and double with twin 
beds for $7, both with baths. The Fairmont Hotel also extends a rate of $4 single 
and $6 double, with bath. Reservations may be made by writing directly to the 
Hotel. 

W. C. KUNZMANN, 

Convention Vice-President 



JOURNAL 

OF THE SOCIETY OF 

MOTION PICTURE ENGINEERS 

Volume XXXV September, 1940 

CONTENTS 

Page 
Television Pick-Up of the Pasadena Rose Tournament Parade 

H. R. LUBCKE 221 



Quality in Television Pictures 

P. C. GOLDMARK AND J. N. DYER 234 



A New Method of Synchronization for Television Systems .... 
T. T. GOLDSMITH, JR., R. L. CAMPBELL, AND S. W. STANTON 254 



Remote Control Television Lighting W. C. EDDY 268 



Mathematical Expression of Developer Behavior 

J. R. ALBURGER 282 



A Modern Studio Laboratory. . . .G. M. BEST AND F. R. GAGE 294 

Current Literature 315 

Fall Convention at Hollywood, Calif., October 21-25, 1940. . . 317 

Society Announcements 322 



JOURNAL 

OF THE SOCIETY OF 

MOTION PICTURE ENGINEERS 



SYLVAN HARRIS, EDITOR 

Board of Editors 
J. I. CRABTREE, Chairman 

A. N. GOLDSMITH A. C. HARDY T. E. SHEA 

J. G. FRAYNB L. A. JONES G. E. MATTHEWS 

A. C. DOWNES E. W. KELLOGG 



Subscription to non-members, $8.00 per annum; to members, $5.00 per annum, 
included in their annual membership dues; single copies, $1.00. A discount 
on subscription or single copies of 15 per cent is allowed to accredited agencies. 
Order from the Society of Motion Picture Engineers, Inc., 20th and Northampton 
Sts., Easton, Pa., or Hotel Pennsylvania, New York, N. Y. 
Published monthly at Easton, Pa., by the Society of Motion Picture Engineers. 

Publication Office, 20th & Northampton Sts., Easton, Pa. 
General and Editorial Office, Hotel Pennsylvania, New York, N. Y. 

West Coast Office, Suite 226, Equitable Bldg., Hollywood, Calif. 
Entered as second class matter January 15, 1930, at the Post Office at Easton, 
Pa., under the Act of March 3, 1879. Copyrighted, 1940, by the Society of 
Motion Picture Engineers, Inc. 

Papers appearing in this Journal may be reprinted, abstracted, or abridged 
provided credit is given to the Journal of the Society of Motion Picture Engineers 
and to the author, or authors, of the papers in question. Exact reference as to 
the volume, number, and page of the Journal must be given. The Society is not 
responsible for statements made by authors. 



OFFICERS OF THE SOCIETY 

* President: E. A. WILLIFORD, 30 East 42nd St., New York, N. Y. 

* Past-President: S. K. WOLF, RKO Building, New York, N. Y. 

* Executive Vice-President: N. LEVINSON, Burbank, Calif. 

** Engineering Vice-P resident: D. E. HYNDMAN, 350 Madison Ave., New York, 
N. Y. 

* Editorial Vice-President: J. I. CRABTREE, Kodak Park, Rochester, N. Y. 

** Financial Vice-President: A. S. DICKINSON, 28 W. 44th St., New York, N. Y. 

* Convention Vice-President: W. C. KUNZMANN, Box 6087, Cleveland, Ohio. 

* Secretary: J. FRANK, JR., 356 W. 44th St., New York, N. Y. 

* Treasurer: R. O. STROCK, 35 11 35th St., Astoria, Long Island, N. Y. 

GOVERNORS 

* M. C. BATSEL, Front and Market Sts., Camden, N. J. 

* J. A. DUBRAY, 1801 Larchmont Ave., Chicago, 111. 
** A. N. GOLDSMITH, 580 Fifth Ave., New York, N. Y. 
** H. GRIFFIN, 90 Gold St., New York, N. Y. 

* P. J. LARSEN, 29 S. Munn Ave., East Orange, N. J. 

* L. L. RYDER, 5451 Marathon St., Hollywood, Calif. 

** A. C. HARDY, Massachusetts Institute of Technology, Cambridge, Mass. 

* H. G. TASKER, 5451 Marathon St., Hollywood, Calif. 

* Term expires December 31, 1940. 
** Term expires December 31, 1941. 



TELEVISION PICK-UP OF THE PASADENA ROSE 
TOURNAMENT PARADE * 

JANUARY 1, 1940 

HARRY R. LUBCKE** 



Summary. The first television pick-up of the Pasadena Rose Tournament Pa- 
rade was made on New Year's Day, 1940. This was accomplished with the "suitcase" 
type portable television equipment and beam transmitter W6XDU of the Don Lee 
Broadcasting System. 

Two television cameras were used to give long-shot and close-up views of the floats, 
the cameras being arranged to give instantaneous switching of scene. The distance 
from Pasadena to the Don Lee Building, site of the home transmitter W6XAO, is nine 
miles and the line of sight was interrupted by two hills and buildings. Since the 
portable transmitter operates on a wavelength of less than one meter, much effort was 
therefore directed toward erecting high and efficient antennas at the transmitter and 
receiver. 

Diathermy machines, as used by the medical profession, were found to cause inter- 
ference even on the beam transmitter frequency of 324 megacycles, indicating the need 
for proper shielding of such devices. 

The sound portion of the broadcast was sent over the nationwide Mutual Network. 
Camera work and aural description were adequately synchronized. Although rain 
fell during the parade and the morning was darkly overcast, written statements of 
reception from W6XAO lookers up to 15 miles away reported clear images, enabling 
them to read the names on the floats and discern other items of detail. 

This paper is concerned with televising the Pasadena Tournament 
of Rose Parade for the first time, on January 1, 1940, by means of 
new portable television pick-up equipment of the Don Lee Broad- 
casting System. 

Prior to the tests over a nine-mile path for the parade pick-up, 
successful operation had been obtained over 2.3 miles. This was 
from the Don Lee Salon on Wilshire Boulevard at Kingsley to the 
Don Lee Building at Seventh and Bixel Streets. In these tests a 
hayrake antenna, as shown in Fig. 1, was used at the transmitter, 
and a double- V antenna, as shown in Fig. 2, was used at the receiver. 

* Presented at the 1940 Spring Meeting at Atlantic City, N. J.; received 
April 15, 1940. 

** Don Lee Broadcasting System, Los Angeles, Calif. 

221 



222 H. R. LUBCKE [J. S. M. P. E. 

The hayrake antenna consists essentially of a folded half-wave di- 
pole fed with a 375-ohm 2-inch spaced feeder and mounted in a V 
reflector consisting of two groups of 3 /Vwavelength-long copper tubes 
separated at an angle of 45 degrees. The double- V antenna consists 
of four half -wave V groups separated one-half wave vertically and 
backed one-fourth wavelength behind by an identical group of re- 
flectors. 




FIG. 1. (Left] Modified hayrake antenna as installed on a 43-foot dur- 
alumin mast at Elks' Club, Pasadena. Mast capable of rotation to orient 
antenna. 

FIG. 2. (Right) Double- V antenna and reflector used in 2.3-mile tests 
and first Pasadena tests. Elevation 18 ft above the roof of a 100-ft build- 
ing. 

With this equipment interference-free images were received, and 
retransmitted over regular television broadcasting station W6XAO 
operating on channel 1 (44 to 50 megacycles). The waves were 
required to pass through or around the Ambassador Hotel. This was 
located about one-third the distance from the transmitter to the 
receiver, and surmounted the line of sight by approximately 30 feet. 

When the identical equipment and antenna were installed and 
operated over the Pasadena Parade path, the signal was very weak. 
The profile of the transmission path gradually fell from Pasadena to 



Sept., 1940] TELEVISION PICK- UP OF PASADENA PARADE 



223 



Los Angeles with two small hills in the line of sight about three miles 
from the latter location (Fig. 3). 

The W6XDU transmitter consists of a 6V4-watt RMA television 
carrier, crystal-controlled unit rated at 324 megacycles. Two camera 

o | "*""" 

,I_J 




FIG. 3. Profile of transmission path from Pasadena to Los Angeles. 

chains, master control, and synchronizing equipment comprise the 
video units. The receiver is a 324-megacycle superheterodyne with 
an intermediate frequency pass-band of 17.5 to 29.5 megacycles. 
This equipment was manufactured by the Radio Corporation of 




FIG. 4. Elks' Club, Colorado Blvd. 
near Orange Grove Ave., Pasadena. 
Transmitting antenna is seen to the right 
of tlie flagpole. 

America, and was the first set of the "suitcase" type that was con- 
structed. 

The transmitting location for the Pasadena tests was the Elks' Club 
building on Colorado Blvd., near Orange Grove Ave. It is shown in 



224 



H. R. LUBCKE 



[J. S. M. P. E. 



Fig. 4. This site was selected because it was in the first portion of 
the line of march, it gave a good elevation for cameras, close prox- 
imity to the antenna, and an absence of tall buildings which would 
shade the street from the sun. 

Antenna Tests. Fig. 4 shows the transmitting antenna at its ulti- 
mate height located just to the right of the flagpole. A close-up of 
the installation is shown in Fig. 1. A P/Vinch duralumin mast 
43 feet high is shown. In the first tests this mast was only 12 feet 
high. In this position and with the transmitter in the open on the 
balcony as shown in Fig. 5 a number of transmitting antenna tests 
were made. 




FIG. 5. Portable television transmitter W6XDU 
and one RCA camera as installed on third floor balcony 
of Elks' Club for parade telecast. 

Several tests were made with the folded dipole in the hayrake re- 
flector array. It appeared to be difficult to feed the antenna properly 
and to cause the high-impedance point to occur at the theoretical posi- 
tion. Serious standing waves existed on the feeder in spite of numer- 
ous adjustments. The junction of the feeder matching section and 
the folded ends of the dipole was consistently the high-impedance 
point, with the physical extremities of the dipole a low-impedance 
point, contrary to theory. The length of the folded dipole was 
altered considerably, with no change in the results. Equally good 
results over the transmission path were achieved by utilizing only 
the folded portions of the dipole as a half-wave antenna of insuf- 
ficient length. The next step was to employ an ordinary half -wave 
antenna in the hayrake reflector 17.2 inches long delta-fed by spreading 



Sept., 1940] TELEVISION PICK-UP OF PASADENA PARADE 225 

the 2-inch-spaced feeders a distance of 7 1 /* inches at the point 
where they fastened to the antenna. With this antenna "grounded" 
at the center to the hayrake reflector the latter was "hot" with 
current. The transmission results were inferior to the original ar- 
rangement. 

The final arrangement consisted of the above half-wave antenna, 
delta-fed but insulated from the hayrake reflector. This arrange- 
ment gave signals of slightly greater strength than the original folded 
dipole, an absence of standing waves on the feeders, and satisfactory 
loading conditions on the transmitter. 




FIG. 5(a). Video equipment inside Elks' Club. Two camera 
monitors and master control monitor on top row; synchronizing 
equipment on bottom row. (Camera and auxiliary unit in fore- 
ground.) 

Rotating the transmitting antenna indicated that it was not emit- 
ting a sharply directional beam. Departure of 30 degrees either side 
of the line of sight to the receiver had little effect upon the received 
signal strength. Subsequent tests proved that being off line of sight 
contributed to this behavior. In contrast, the double- V receiving 
antenna gave a sharp maximum signal within == 5 degrees of the line 
of sight. 

The first step toward improving the signal-to-noise ratio was the 
erection of a 15-wavelength V antenna. The central angle was 25 
degrees. The extremity of each wire of the V, which was approxi- 
mately 45 feet long, was terminated in a two-turn 1 / 2-inch diameter 
coil, a 400-ohm non-inductive resistor, and half -wave rod 18 inches 
long mounted vertically. Victron insulation was used for feeder 



226 



H. R. LUBCKE 



rj. S. M. p. E. 



spacers and other insulation points. All the tests made to date 
have been with horizontal polarization. The vertical half-waves on 
the V antenna thus intercepted a minimum of energy and acted as 
efficient "grounds." 




FIG. 6. ( Upper} Twenty-wavelength V antenna. Free 
ends at center, feeder at right. Elevation 33 ft above the roof 
of a 100-ft building. 

FIG. 7. (Lower} Hayrake receiving antenna, lower center. 
Elevation 51 ft above the roof of 100-ft building. Twenty- 
wavelength V antenna upper center. Elevation 100 ft above 
100-ft building. 

This antenna was 15 feet higher than the former double- V receiv- 
ing antenna of Fig. 2, mounting to 33 feet above the top of a 100-foot 
building. The antenna was supported at three points by ropes, 
as shown in Fig. 6. By means of pulleys the antenna could be steered 
to the necessary line of sight. 



Sept., 1940] TELEVISION PICK-UP OF PASADENA PARADE 227 

This antenna gave a considerably stronger signal than the double- 
V. It was quite directional. With the original angle of 25 degrees, 
maximum signal was obtained when the west wire of the V was al- 
lowed to sag about 10 feet lower than the east wire. The next step 
was to vary the angle of the V. Decreasing the angle definitely re- 
duced the signal. The next operation was to increase the length of 
the antenna to 20 wavelengths by adding 14.3 feet to each wire. 
This effectively narrowed the angle and no signal increase was noted. 
The opening of the V at this time was 13 feet. Increasing this open- 
ing 6 feet to 19 feet gave twice the former signal. At this point 
moving automobiles and bleachers along Colorado Boulevard were 
discernible. Increasing the width of the V by 3 feet more gave a fur- 
ther increase in signal and required that the west and east wires be 
at the same height to obtain maximum pick-up. This indicated 
that the former slack position of the west wire was an artifice that 
effectively increased the angle of the V. 

The next operation was to change the lengths of the wires of the V. 
By removing 3 inches from both wires the signal again doubled. The 
final length of each wire of the V antenna was 57 feet and the separa- 
tion at the wide end 30 feet, which corresponds to an angle of 31 de- 
grees. It was interesting to note that the best results were at- 
tained with such a small change of length as 3 inches in 57 feet, and 
that the angle was considerably greater than the theoretical value 
of 25 degrees. The directivity of the antenna was definite. 

Although this antenna gave reasonably good images it was de- 
cided to test it against a hayrake receiving antenna. This was 
composed of a prescribed hayrake assembly, as described above, 
with a folded dipole shortened to 18 inches total length, as former 
transmitting tests had indicated as optimal. This installation is 
shown in the lower central part of Fig. 7. This was mounted at an 
increased height of 18 feet over the former V, or a total of 51 feet 
above the roof of the 100-foot building. A pivot arrangement was 
provided at the top of the wooden mast so that the direction of the 
antenna could be changed. These ropes are shown in Fig. 7. In 
spite of the greater height the signal was approximately the same as 
with the former V antenna. Orienting the antenna did not change 
the signal strength appreciably. 

At this point the transmitting antenna was raised by another 
section of duralumin mast, increasing the height from 12 to 24 
feet above the building of Fig. 4, which is approximately 50 feet high. 



228 H. R. LUBCKE [J. S. M. P. E. 

This doubled the received signal strength. The considerable signal 
increase from the small increment in height was caused by raising 
the line of sight just above certain trees and frame residences about 
one mile from the transmitter. The two hills still intervened, how- 
ever. 

The final reception antenna change consisted in increasing the 
height of the formerly adjusted V antenna to 100 feet off the roof, 
making it 200 feet off the ground. This is shown in the upper part 
of Fig. 7, with the open ends of the Fnear the tower and "skyrope," 
respectively, and the top end of the feeder at the top edge of the 
photo. This change increased the signal strength three more times. 

The final antenna change was made at the transmitter, where 
somewhat more than I 1 / 2 sections of duralumin mast were added, 
building the total height to 43 feet, as shown in Fig. 4. This again 
doubled the received signal strength. With these increased heights 
the profile along the line of sight was definitely raised but the results 
were such as to indicate substantial obstacles still in the path, at least 
a few buildings. 

To summarize, it can be said that a V antenna proved the most 
satisfactory as regards gain and directivity, that the hayrake antenna 
was less satisfactory, and that the double- V antenna was compara- 
tively satisfactory. In all cases, the additional loss of feeder at the 
receiver and at the transmitter had no effect compared to the in- 
creased signal resulting from the additional height. In this one 
path at least, the height of the receiving and transmitting antennas 
was the most important factor in obtaining adequate signal strength. 

Incidentally, it was found that the television cameras could be 
located as close as ten feet from the transmitter and feeder to the an- 
tenna without radio frequency feedback. The antenna was 40 feet 
away airline, higher, and pointing away from the cameras. 

Interference. The most apparent interference was the thermonic 
noise of the intermediate frequency stages of the television beam re- 
ceiver. Fundamental research on reducing this noise would have a 
definite effect upon increasing the maximum range of the portable 
equipment. 

Surprisingly, diathermy medical machine interference was experi- 
enced on the ultra-high-frequency of 324 megacycles. It was tun- 
able by adjusting the oscillator frequency of the receiver. This indi- 
cates that the energy received was approximately at 324 megacycles, 
and not in the 17.5 to 29.5 intermediate-frequency band of the re- 



Sept., 1940] TELEVISION PICK-UP OF PASADENA PARADE 229 

ceiver. It was also found that diathermy interference could be neu- 
tralized in certain instances by carefully orienting the V antenna. 
The effect of diathermy interference was great on the nine-mile 
Pasadena pick-up. On the 2.3-mile test diathermy herringbone pat- 
terns had been noted. These were undoubtedly the same machines, 
but of less effect because of the greater signal strength. Many per- 
sonal and telephone calls to suspected locations did not locate the 
sources. Further tests by the diathermy-locating automobile of 
the Television Service Engineers of Los Angeles also could not locate 
the sources. The diathermies usually had a fundamental of about 
25 megacycles, and simultaneously interfered with 45.25-megacycle 
television reception in the Don Lee Building. 

Another serious interference in this particular installation was the 
900-kc radio-frequency energy of radio broadcasting station KHJ. 
At the maximum, with the 100-foot V antenna, 1 / 3 ampere of radio- 
frequency current flowed in the V feeders. This was reduced to a 
considerably smaller value by placing 150-MM / mica condensers in 
each feeder at the receiver. The feeder length was also adjusted by a 
few inches to give maximum signal-to-noise ratio. The condensers 
had a "quarter- wave effect" of nine inches effective length as would 
be expected. 

A quarter- wave "short" to all frequencies other than 324 mega- 
cycles was also utilized. This was composed of a 9-inch length of 
wire from each feeder at the receiver terminals to ground. Tests 
indicated that this had no effect upon the received signal strength but 
served to remove residual pick-up of television station W6XAO in the 
beam receiver. 

This short did not have appreciable effect upon KHJ interference. 
The ground configuration at the receiver had a large effect upon the 
KHJ pick-up. The best ground was obtained by running a No. 12 
wire to the iron ladder shown in the rear of Fig. 8. A change of a 
few inches in the length of this lead would greatly alter the amount of 
KHJ interference. 

A further manifestation of KHJ interference was inherent in the 
video line of approximately 125 feet from television beam receiver to 
W6XAO transmitter. It was necessary to locate the beam receiver 
at this distance from the transmitter in order to avoid feedback at 
the high gain setting necessary in this nine-mile pick-up. The re- 
ceiver is shown in Fig. 8 as installed in an elevator penthouse on the 
Don Lee Building. 



230 



H. R. LUBCKE 



[J. S. M. P. E. 



Four different video line configurations were installed. The first 
was a copper-braid shielded rubber-insulated 72-ohm coaxial con- 
ductor, which was run beneath a 1-inch conduit on the ceiling of the 
eighth floor of the Don Lee Building. The sheath was insulated from 
all objects, and by grounding at the transmitter end a minimum of 
pick-up resulted. 

A second line on the ceiling of the seventh floor of the Don Lee 
Building was considerably inferior to the above line. It was expected 

that the reverse would be true because 
the KHJ and W6XAO transmitters 
are located on the eighth floor with 
the antennas on the roof. 

The third line consisted of the same 
sheathed coaxial line lying on the roof. 
The fourth line, also on the roof, was 
composed of 3 /4-inch thin-walled con- 
duit with fabric loom inside, with the 
above coaxial cable pulled through it. 
This gave double insulated shielding 
throughout the length of the run. 
The receiver end can be noted com- 
ing into the window at the left of 
Fig. 8. In the final arrangement the 
conduit was not grounded at any 
point, but the outer sheath of the 
coaxial conductor was grounded at 
both ends of the run. 

A further type of interference was 
caused by the sparking of heavy ele- 
vator controls in the same building 
with the beam receiver. These contacts broke between 200 and 500 
amperes. The most important effect on the signal was a 200 per 
cent change of the d-c level. The current broken was d-c ; the re- 
ceiver was operated on a separate single-phase a-c line. This was 
eliminated during the parade by not operating the elevator. 

Parade Conditions. A normal winter-light intensity for Los 
Angeles is from 250 to 650 on a Weston brightness photometer of the 
usual type (measuring brightness in foot-candles per square-foot). 
Tests with the portable pick-up equipment had shown that light- 
ing of 80 was necessary to give a good image. 




FIG. 8. Beam receiver, 324 
mcs as installed on roof of Don 
Lee Building for parade telecast. 



Sept., 1940] TELEVISION PICK-UP OF PASADENA PARADE 231 

The morning of the parade was very dark and overcast, giving a 
reading throughout of 40. The parade started promptly at 9:15 
A. M. and concluded at 1 1 :00 A. M. During the last half of the parade 
it was raining, from medium to light intensity. At home receivers 
seven miles from W6XAO it was possible to see the wet streets at 
certain camera angles before the announcer admitted it was raining. 
In Figs. 9 and 10 the papers on the heads of the spectators and the 
covers on the equipment indicate the conditions. 

Because the day of the parade was a holiday the background inter- 
ference over the relay link was approximately half that of a normal 
working day. This fact, combined with operation at maximum 
camera sensitivity and continued attention to shading adjustments, 
made the picture satisfactory. In Fig. 9., for instance, on home re- 
ceivers it was not difficult to see the girl on the front of the bell of the 
float shown. The bell rocked, back and forth. The contrast be- 
tween the bell and the girl was small, as can be noted in the photo- 
graph. It was possible to read the names on all the floats save one, as 
reports as far as fourteen miles from transmitter W6XAO so stated. 

Operative Set-Up. The televising of the parade was done in con- 
junction with the aural broadcast sent over the nationwide Mutual 
network. There existed a dual problem in synchronizing camera 
operations with word description of the event and the proper aural 
presentation for a nationwide audience. Two motion picture trained 
television cameramen, McEdwards and Warren, operated the cam- 
eras. One camera had a 6 l /2-hich//3.5 lens and the other a 19-inch 
//4 telephoto lens. The camera pick-ups were viewed and shaded by 
television engineers Pitzer and Jury. The former also monitored the 
transmitter W6XD U adjustments and the latter switched cameras at 
the master control unit. He was provided with double headphones, 
one of which gave out instructions and the other the network sound 
output. A breast-type telephone transmitted his instructions to the 
cameramen. There was also a television production supervisor, 
Sawyer, assistant, Waldegrave, two announcers, Albright and Young, 
two sound engineers, Kennedy and Murray, and a radio production 
supervisor, Van Newkirk. 

The point of greatest nervous intensity was at the master control 
unit. The network announcers were allowed to describe the parade 
as they saw it, with general instructions as to the tempo of their de- 
scription. It was necessary to have their description of a particular 
float end as the float reached the limit of the camera panning range. 



232 



H. R. LUBCKE 



[J. S. M. P. E. 




FIG. 9. ( Upper} Parade scene. San Gabriel float. Camera- 
man McEd wards right, producer Waldegrave left. 

FIG. 10. (Lower} Parade scene. Note wet streets and 
papers over heads of spectators in grandstands. Aural broad- 
cast personnel at right foreground. 



Sept., 1940] TELEVISION PICK-UP OF PASADENA PARADE 233 

The usual technic was to establish the existence of a float and sur- 
roundings by the wide-angle 6V2-inch lens, and then to follow it 
from an advance position to a point somewhat beyond the location of 
the camera with the 19-inch lens. During this time the announcer 
gave the description and interesting notes pertaining thereto. The 
images from the telephoto camera were of greatest clarity, since this 
restricted the field of view to about 20 feet in width at the closest 
position. The wide-angle camera showed several hundred feet of 
the street and included the grandstand, trees, and sky as well. Tele- 
photo shots of a single individual as in Fig. 10 were quite satisfactory. 
There was, of course, over the relay link a background of interference 
noise because of low signal strength. 

Acknowledgment. The assistance of Henry Rhea, Dr. G. Brown, 
and W. Beltz of RCA is gratefully acknowledged in testing the 
equipment on the 2.3-mile pick-up. The generosity of the Pasadena 
lodge of Elks in opening their club to television was greatly appre- 
ciated. The untiring work of the television staff, Thorp, Klein, 
Jury, Pitzer, Wyland, and O'Brien, and the cooperation of the radio 
broadcasting department under F. Kennedy are likewise acknowl- 
edged. 



QUALITY IN TELEVISION PICTURES* 
P. C. GOLDMARK AND J. N. DYER** 

Summary. Present television standards specify certain factors which determine 
the appearance of a television picture only to a limited extent. Other factors, how- 
ever, such as contrast, gradation, brilliance, and the shape of the scanning spot, are 
fully as important. 

A photographic method for producing artificial television pictures which permits 
varying several of these factors has been developed. Pictures are shown which were 
obtained by this method and which approach ideal quality within a given set of stand- 
ards. 

This paper is a summary of recent investigations and experiments 
aiming to determine the best possible television picture quality that 
would be available within the so-called RMA television standards. 

Equipment has been designed to duplicate photographically the 
appearance of a television picture with predetermined characteristics, 
such as definition, contrast, and gradation. 

The following factors chiefly determine the quality of a television 
picture : 

(1} Definition. 

(2) Contrast range. 

(5) Gradation. 

(4} Brilliance. 

(5) Flicker. 

(6} Geometric distortion. 

(7) Size. 

(8) Color. 
() Noise. 

Of the nine factors determining the picture quality only the first, 
definition, and the fifth, flicker, are subject to standardization, and 
these will be dealt with first. 

Definition. When viewing objects which are comparatively dimly 
lighted, such as television pictures, the iris of the human eye is ex- 

* Presented at the 1940 Spring Meeting at Atlantic City, N. J. ; received May 
3, 1940. 

** Columbia Broadcasting System, New York, N. Y, 
234 



QUALITY IN TELEVISION PICTURES 



235 



panded in order to allow maximum light to enter the eye, resulting in 
reduced visual acuity. 

Under ordinary conditions the overall resolving power of the eye 
is limited to the spacing of the cones on the fovea, which has been 
found to be about 0.01 mm. 1 As a result the resolving power of the 
eye will not be better than 1 minute. Tests have shown that on the 
average the minimum resolving angle is between 1.3 and 1.5 minutes 
of arc at light intensities to be expected in television. 



3 
Z 

I i 



VISUAL ACUITY IN Mil 

OF ANCLE. 
NUMBER OF LINES. 

VIEW.Ng DISTANCE 
PICTURE HEIGHT 




441 LINES 

625LINES 
700UNES 



f, 6 /o 

VIEWING DISTANCE 
PICTURE HEIGHT 



FIG. 1. 



Visual acuity vs. ratio of viewing distance to pic- 
ture height. 



For motion pictures the most satisfactory viewing angle, that is, 
the angle subtended by the eye of the observer and the edges of the 
picture in the horizontal direction, has been found to be not more 
than 20 degrees. This corresponds to 15 degrees in a vertical plane 
for a picture ratio of 3:4. Due to the limited angle of sharp vision, 
all parts of the picture could not be seen satisfactorily at the same 
time if the viewing angle were larger. 

Visual acuity varies from one individual to another and so does the 
most satisfactory viewing distance. A relationship between visual 
acuity, number of lines per picture, and various ratios of viewing- 
distance-to-screen-height was developed on the assumption that the 
vertical and horizontal details are approximately equal (Fig. 1). Re- 
gardless of whether the line structure is apparent due to improper 



236 P. C. GOLDMARK AND J. N. DYER [J. S. M. P. E. 

scanning spot size or shape, this relationship must be applied in view 
of the limitation on detail imposed by the available frequency band 
of the television system. 

The diagram in Fig. 1 indicates that for a 441 -line picture and a 
visual acuity of 1.5 minutes, a viewing distance to height ratio of 
5.7/1 is desirable. Design characteristics of modern motion picture 
theaters show that satisfactory viewing conditions are obtained up 
to distances as much as 12 times the picture height. 

It is desirable to determine how much visual detail may be repro- 
duced by a television system with a given number of lines and fre- 
quency response. This may be analyzed mathematically, but for 
some purposes it would be more satisfactory actually to produce an 
idealized television picture. Such pictures, though they could prob- 
ably not be duplicated by commercial receiving and camera tubes 
today, would be very useful tools in indicating the capabilities of a 
given set of television standards. 

The maximum definition that a television system is capable of 
reproducing is determined not only by the frequency response of the 
entire system but also by the receiving and transmitting scanning 
spots, the number of scanning lines and frames, and the fine detail 
contrast. Electron scanning beams of circular cross-section and non- 
uniform current distribution are ordinarily used at present in the 
camera and at the receiver. The shapes of these scanning spots, 
therefore, become important factors in determining definition. The 
effect of a particular frequency response characteristic on the fine 
detail has been shown to be the same as that of an equivalent scanning 
spot. For example, the effect of an infinitely narrow scanning spot 
and a given finite frequency characteristic could be duplicated by a 
properly designed scanning spot used with an amplifier with a flat 
response to an infinite frequency. Such a scanning spot may not 
always be physically realizable, particularly in cases where there is a 
sharp cut-off in the frequency characteristic of the electrical system 
(Fig. 2). 

It has been shown that if the frequency response of a television 
system follows the shape of a probability curve e~ x \ the equivalent 
scanning spot distribution will follow a similar curve. 2 It was de- 
cided to use this type of characteristic to produce the synthetic pic- 
tures. The cut-off point of any frequency characteristic has been de- 
fined as the upper limit of a rectangular characteristic of equivalent 
area. Under present-day television standards the receiver band 



Sept., 1940] 



QUALITY IN TELEVISION PICTURES 



237 



width is limited to about 4.25 me and the response must be zero at 
4.5 me. The pictures which have been produced have assumed a cut- 
off frequency as previously defined of 4.25 me with a response charac- 
teristic which follows a probability curve. The closest approach to 
this characteristic which can be made with the present standards 
would follow the probability characteristic to the cut-off frequency 
and would then drop rapidly to zero. This would result in small 
oscillatory transients which would only be about =*= 5 per cent of the 
peak signal value on scanning from a black to a white area. (It 



20 25 30 35 40 

/.OF 13 kC PERIOD 



50 55 60 65 



FIG. 2. 



Calculated response to suddenly applied voltage 
of idealized 75- kc low-pass filter. 



must be noted that the transient may build up to larger amplitudes if 
the picture consists of a number of parallel vertical lines at the proper 
spacing.) It is difficult to say whether or not this is a desirable or 
tolerable condition since most practical experience up to this time has 
been with television systems where the scanning spots have been large 
enough to mask transients of this type which otherwise might be 
seen. 

The frequency response characteristic of the electrical system today 
is only responsible for a small part of the total loss in detail if the 4.25 
me band width is being fully utilized. Major causes for loss of defini- 
tion today are incorrect scanning spot shapes at the receiving tube 
and, to a lesser degree, in the pick-up tube. Low contrast in the fine 



238 P. C. GOLDMARK AND J. N. DYER [J. S. M. P. E. 

detail reduces the apparent definition at the receiver. Variation in 
spot size with current intensity impairs the resolution of the final 
image and limits the maximum useful brilliance of the picture. 

Contrast Range. It has been found that a projected motion picture 
or a good photograph can provide a satisfactory rendition of most sub- 
jects with a contrast range of about 35 to 1. 

Measurements of present-day cathode-ray tubes as used in tele- 
vision receivers show that the maximum contrast range is usually 
about 30 to 1. (Such ranges are obtained only in darkened rooms and 
between widely separated areas on the tube screen.) The contrast 
range between two adjacent points on the screen is not ordinarily more 
than 10 to 1. Extension of the contrast range to 30 to 1 in the 
fine detail would certainly more than double the subjective quality of 
present-day pictures. Observations indicate that more contrasty 
pictures seem to create the impression of better definition. 

The most important factors impairing a satisfactory contrast range 
are : halation on the fluorescent screen, curvature of the screen and 
reflections within the bulb itself. 3 The contrast range is reduced if 
extraneous light falls on the cathode-ray tube screen as is often the 
case under average viewing conditions. In order to extend the con- 
trast range under such conditions it is necessary to increase the maxi- 
mum brilliance of the picture. 

It is important to realize that the resolution is also limited by in- 
correct scanning beam spot sizes and shapes. Cathode-ray tubes 
of today achieve fairly good horizontal resolution by employing a 
small round spot, the diameter of which is less than the theoretical 
width of one line. The theoretically correct shape for a spot would be 
that of a rectangle, its height being equal to 1/441 of the picture height 
and its width, that is, its dimension in horizontal direction, being a 
fraction of its height. Since the area of such an ideal spot is greater 
than that of the small circular spot, the maximum brilliance of the 
narrow rectangular spot of correct height would be greater by the ratio 
of the respective areas, provided the current densities remain the 
same. 

Gradation and Brilliance. It is ordinarily assumed that the eye re- 
sponse is logarithmic. A picture can not represent reality in all re- 
spects, and usually it is impracticable to reproduce the average 
brightness of the original scene. Under such conditions it is impor- 
tant that correct rendition of brightness differences be obtained over 
the entire contrast range. This condition is satisfied when the gradi- 



Sept., 1940] 



QUALITY IN TELEVISION PICTURES 



239 



ent of the television system is constant regardless of the brightness. 

The gradient of a television system may be denned as the ratio 
A log B T / A log B t where B r is the brightness of the receiver cathode- 
ray tube and B t is the brightness of the transmitted scene. The gamma 
of a television system is equal to the gradient over the straight-line 
portion of the log B T vs. log B t characteristic. 

Television systems today do not necessarily maintain a constant 
gradient over the entire operating characteristic. This results in the 
appearance of crowding of the tone range in the blacks or whites, or 
both. Pictures have been produced in the laboratory where the 



Object Illumination: 0.87 Ft-c 



Illumination of Surroundings 
(Foot-Candles) 




1.0 

Perceptible flicker frequency vs. illumination of surround- 
ings. 



gradation was approximately correct and it can be expected that an 
improvement in this respect may be achieved without great difficulty. 

The average brightness of a television picture should probably be 
about 8 apparent foot-candles. This would correspond to highlights 
of the order of 17 apparent foot-candles, depending on the composition 
of the picture. Though visual acuity improves somewhat with bril- 
liance, an increase in illumination of 2:1 will change only slightly the 
relationship between visual acuity and number of lines. An increase 
in picture brilliance will automatically extend the contrast range and 
improve the gradation. 

Flicker. It is recognized that the brilliance of present cathode- 
ray pictures is inadequate for viewing in undarkened rooms. Tele- 



240 P. C. GOLDMARK AND J. N. DYER [J. S. M. P. E. 

vision pictures scanned at a rate of 15 or even 24 frames per second 
(interlaced scanning), which do not display flicker up to approxi- 
mately 6 foot-candles, will show conspicuous flicker at higher brilli- 
ancies. The frame repetition rate of 30 per second (interlaced) as 
used in television today is well justified because flicker is a more seri- 
ous problem in television than in motion pictures for the following 
reasons: First, assuming that the integrated light is constant, flicker 
will increase in proportion to the ratio of the dark period to the light 
period. 4 Second, it is desirable to view television in undarkened 
rooms and therefore brilliancies greater than found on motion picture 
screens will be required. Third, the higher the illumination of the 
surroundings in which the television picture is viewed, the more flicker 




FIG. 4. Artificial television scanner. 

will be perceptible. The diagram shown in Fig. 3, which is based on 
experimental results, 5 shows that with 0.001 foot-candle illumination 
of the surroundings and 0.87 foot-candle illumination of the picture 
under test, flicker just becomes perceptible at about 21 field changes 
per second. With the same picture illumination but with a surround- 
ing illumination of 1 foot-candle, the field repetition rate has to be in- 
creased to 34 per second in order to eliminate flicker. Low frame fre- 
quencies can be employed successfully only in conjunction with a 
storage method which retains the received image for the duration of a 
complete frame (including the blanking period). 

There is some difference of opinion as to whether a reduction in pic- 
ture repetition rate may be desirable if complete storage were pos- 
sible. There will be some sacrifice in the appearance of motion as the 
repetition rate is reduced, but with a given frequency band increased 
detail will result. When satisfactory storage methods are found ex- 



Sept., 1940] 



QUALITY IN TELEVISION PICTURES 



241 



periments will undoubtedly show the most desirable repetition rate 
under any given set of conditions. 

Geometric Distortion, Size, and Color. Geometric distortion can be 
caused by lens distortion in the cameras, scanning distortion in the 
cameras, scanning distortion, and curvature of screen at the receiving 
tube. The trend toward cathode-ray tubes with flat screens in con- 
junction with accurate scanning will eliminate most of the distortion 
existing at present. 




FIG. 5. Artificial television scanner partially disassembled. 



The minimum height of a 441 -line television picture is about 2 
inches since it is determined by the minimum comfortable viewing dis- 
tance of about 15 inches (Fig. 1). The upper limit is determined by 
how much viewing distance is available. Motion picture experience 
has shown that for minimum eyestrain the screen height should be not 
more than 0.27 times the viewing distance regardless of the amount of 
detail. This value is therefore independent of the number of lines in 
a television picture. 

Most television picture tubes today have a screen material which is 
satisfactory from a color point of view, that is, highlights are repro- 



242 



P. C. GOLDMARK AND J. N. DYER [J. S. M. P. E. 



LIGHT SOURCE 



CONDENSER 



POSITIVE TRANSPARENCY 



LENS 
APERTURE I 



duced as pure white. Though greater efficiency can be obtained from 
other than white screen materials, the latter is preferable for the sake 
of its color in projection tubes. 

Artificial Television Scanner. An apparatus was constructed to 
duplicate the behavior of an ideal television system by photographic 
methods. Positive transparencies of desired subjects were prepared 
on 8 X 10-inch glass plates. These positives were then scanned with 

a moving light-source and optical 
system, one line at a time, and 
were reproduced on a sensitized 
photographic plate. The hori- 
zontal scanning was motor-driven 
with automatic limit switches and 
braking. The change in the 
direction of scanning at the end 
of each line and the advancement 
in the vertical direction were 
manual, and the latter was ad- 
justable for any desired number 
of lines. Alternate lines could be 
scanned in opposite directions 
since the denning apertures were 
symmetrical (Figs. 4 and 5). 

The definition was determined 
by the apertures in the optical 
system. The optical system con- 
sisted of a light-source with a condenser lens above the positive 
plate to be scanned and two lenses of V2-inch focal length 
assembled in a housing and located between the positive and 
the sensitive plates. Two apertures were used in the optical sys- 
tem with one aperture placed just above the lower Yz-mch lens and 
one just below the upper lens. The image of the positive was focused 
on the lower aperture which might be termed the frequency response 
aperture. The upper aperture represented the receiver or transmitter 
spot size and was focused on the photographic plate (Fig. 6). 

The number of lines was determined by the size of the spot in the 
vertical direction and by the amount by which it was advanced verti- 
cally at the end of each line. The optical system was arranged to give 
a 2 : 1 reduction of the image of the upper aperture and a corresponding 
enlargement of the image focused on the lower aperture. This made 



APERTURE 2 
LENS 



NEGATIVE TRANSPARENCY 



FIG. 6. Optical system. 



Sept., 1940] 



QUALITY IN TELEVISION PICTURES 



243 



it possible to make the very small apertures twice the size they other- 
wise would have been. 

Some of the fundamental requirements of apertures designed to re- 
produce the effect of a given frequency response have already been 
described. The ideal aperture of the e~* 2 type would be rectangular 
and of a height equal to one scanning line with a light transmission 
across its width corresponding to a probability curve (Figs. 7 and 8; 
Fig. 8 shows aperture dimensions for the particular optical system 
described above). 



RELATIVE HEIGHT 

_ ro w * CM '-4 oo io b 




















4 
4 
6 


41 LINES 15% BLANKING 2.5MC-BAND WIDTH 
41 LINES 15% BLANKING 4.25 MC-B AND WIDTH 
65 LINES 15% BLANKING IOMC' BAND WIDTH 


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.1 .2 .4 .6 .8 1.0 \Z 1.4 1.6 1.8 2.0 22 2.4 2.6 2.8 3.0 

PICTURE WIDTH x I0' s 



FIG. 7. Aperture shapes for duplicating receiver response based on response 
shaped like probability curve e~* 2 . 



Attempts were made to produce apertures by photographing large- 
scale models. However, it was immediately apparent that the dis- 
persion of even the finest-grained emulsion could not be tolerated be- 
cause of the great loss in light. An alternative approximation was to 
shape the leading and trailing edges of the aperture so that the de- 
sired characteristic could be obtained. The characteristic could be 
quite well approximated by assuming it to be a straight line. It was 
essential that the density in the vertical direction across a scanning 
line be constant in order to minimize the line structure. The aper- 
ture shape that immediately suggested itself was a parallelogram. 
A comparison between the theoretical aperture e~ x * and the parallelo- 



244 



P. C. GOLDMARK AND J. N. DYER [J. S. M. P. E. 




441 LINES 2.5 MC- 30 FRAMES 



441 LINES 4.25 MC- 30 FRAMES 



[ 665 LINES 10 MC- 30 FRAMES 
[ 625 LINES 4.25 MC- 15 FRAMES 



FIG. 8. Aperture sizes for duplicating receiver response 
based on probability function e~ xZ . 




FIG. 9. Calculated aperture response for suddenly 
encountered white picture area. 



Sept., 1940] QUALITY IN TELEVISION PICTURES 



245 



TRANSMISSION 




IDEAL APERTURE TYPE-A 



X DIMENSION ALONG DIRECTION OF SCANNING 

TYPE-B 







TYPE-C 



TYPE-D 



FIG. 10. Types of apertures for duplicating receiver 
response. 




DIRECTION 
OF SCANNING 



FIG. 11. Arrangement of aper- 
tures to simulate effect of fre- 
quency response (receiver and 
transmitter spots narrow' rec- 
tangles). 




DIRECTION 
OF SCANNING 



FIG. 12. Arrangement of aper- 
tures to simulate effect of fre- 
quency response and receiver 
spot size. 



246 



P. C. GOLDMARK AND J. N. DYER [J. S. M. P. E. 



gram apertures which were used shows that there is little difference in 
their behavior (Fig. 9) . 

The parallelogram would give the desired effect when scanning 
across vertical lines, but on encountering a line tilted at the same angle 
as the edges of the aperture, it would produce too much detail. This 
effect could be minimized by dividing up the aperture into several 







FIG. 13. Original photograph from which Fig. 14 was produced. (Photo 
by Fair child Aerial Surveys.) 

parallelograms. An infinite number of parallelograms would be 
ideal, but practically it was found that three would give adequate 
results (Fig. 10). 

Simulated television photographs were made of several typical 
subjects and two conditions were studied with the aid of the scanner. 
The first condition is the very ideal situation where the receiver and 
the transmitter spots are rectangular slits exactly one line high and 
where the frequency response is duplicated by one probability aper- 
ture (Fig. 11). 



Sept., 1940] 



QUALITY IN TELEVISION PICTURES 



247 



For the second condition, which might be considered to be more 
realizable today, it was assumed that only the transmitting aperture 
was of the ideal narrow rectangular shape and that the receiving 
aperture, while considerably better than in most present-day tubes, 
was not ideal. The current in the transmitting scanning beam is 
ordinarily very low, and it can be expected that the ideal shape might 




FIG. 14. 



Scanned reproduction of Fig. 13 (441 lines, 30 frames, 4.25 megacycles, 
slit aperture) . 



be approached. It was assumed that the receiving spot intensity 
could be made uniform in the vertical direction and approximately 
one line width high, but the horizontal distribution was the same as 
in the frequency response aperture (Fig. 12). 

Reproductions of pictures produced by the artificial method are 
shown in Figs. 13 to 16. A 441 -line scanning standard was used with 
a cut-off frequency of 4.25 me (assuming 30 frames per second). Fig. 
14 was produced with the apertures arranged as in Fig. 11 and as- 
sumed that the receiver and the transmitter spots were narrow slits, 



248 P. C. GOLDMARK AND J. N. DYER [J. S. M. P. E. 

exactly one line high. Fig. 13 is the original photograph from which 
Fig. 14 was made. The pictures shown in Figs. 15 and 16 were 
produced using the aperture arrangement of Fig. 12 and simulated a 
television system where the horizontal distribution of the receiving 
spot followed the e~ x * shape. The distribution across the spot in 
the vertical direction was uniform. Some of the pictures show spuri- 




FIG. 15. Scanned picture (441 lines, 30 frames, 4.25 megacycles, t~ 

aperture) . 



ous patterns of the type predicted by Mertz and Gray, but it should 
be realized that this effect is not uncommon since it is produced by all 
halftone processes. Defects of this type will be less noticeable when 
objects are in motion. 

Conclusion. The synthetic pictures seem to indicate that television 
pictures as received today have to be improved a great deal before the 
capabilities of present 441 -line standards are fully utilized. 



Sept., 1940] QUALITY IN TELEVISION PICTURES 249 

The authors would like to express their appreciation of the large 
amount of work contributed to this project by Messrs. Doncaster, 
Hollywood, Piore, and the other members of the CBS Television De- 
partment. 




FIG. 16. Scanned picture (441 lines, 30 frames, 4.25 megacycles, e~ x2 

aperture) . 



REFERENCES 

1 HARDY, A. C., AND PERRIN, F. H.: "The Principles of Optics," p. 190. 

2 WHEELER, H. A., AND LOUGHRAN, A. V.: "The Fine Structure of Television 
Images," Proc. I. R. ., 26 (May, 1938), p. 540. 

MERTZ, F., AND GRAY, P. : "A Theory of Scanning and Its Relation to the 
Characteristics of the Transmitted Signal in Telephotography and Television," 
Bell Syst. Tech. J., 13 (July, 1934), p. 464. 

3 LAW, R. R.: "Contrast in Kinescopes," Proc. I. R. E. (Aug., 1939), p. 511. 

4 IVES, H. E.: "Critical Frequency Relations in Scotopic Vision," /. Opt. Soc. 
Amer., 6, (1924), p. 2548. 

Ibid.: "A Theory of Intermittent Vision," /. Opt. Soc. Amer., 6 (1924), 
p. 343. 



250 P. C. GOLDMARK AND J. N. DYER (J- $ M. P. E. 

COBB, P. W. : "The Dependence of Flicker on the Dark-Light Ratio of the 
Stimulus Cycle," /. Opt. Soc. Amer. (April, 1934). 

6 LYTHGOE, R. J., AND TANSLEY, K. : Med. Counc. Spec. Rep., Ser. No. 134 
(1929). 

DISCUSSION 

MR. F. H. RICHARDSON: We have just been told that television is next door 
to the theater. What is the prospect of serving the entire country through tele- 
vision in the theater? 

MR. DYER: That depends upon much more than engineering. It obviously 
has a lot to do with economics. No one today is going to put money into a tele- 
vision network to cover the United States in the way that a group of chain theaters 
does, although the engineers probably have adequate and satisfactory methods for 
covering the country with television facilities. It is going to be a long time before 
that happens. 

MR. BEERS: When the motion picture industry turned to sound-on-film it 
adopted the film speed of 24 frames a second. It has been said that even if that 
speed were not required for satisfactory reproduction of sound, the industry 
would still adhere to it on the basis of the improvement obtained in reproduction 
of motion. Is that fact or fiction? 

DR. GOLDSMITH: As I understand Mr. Beers's question, if the motion 
picture industry were not concerned with adequate sound reproduction at 90 feet 
per minute, and if the film users and manufacturers were not interested in the 
additional film footage thus used, and if the sole criteria were excellence of picture 
quality, absence of flicker, and smoothness of depicted motion, would the industry 
still adhere to 24 pictures or 48 fields per second, rather than the supposed former 
practice of 16 pictures and 32 fields per second? 

MR. DUBRAY: Sixteen pictures a second proved satisfactory for silent films. 
The film speed of 60 feet a minute was found to be the minimum speed necessary 
to eliminate flicker under normal screen brightness and with a view to economy of 
film. 

MR. BEERS: I am not interested in flicker, but in the reproduction of motion. 
Is the improvement obtained in going from 16 to 24 frames, judged only from the 
standpoint of the reproduction of motion, worth the additional cost of making the 
change? 

MR. DUBRAY: Camera and projector speeds are, of course, closely related, and 
for faithful reproduction the projector should operate at the same speed as the 
camera. Flicker is a major consideration for determining film speed. For a 
static object a speed of 60 feet a minute would be satisfactory. For rapidly mov- 
ing objects, greater speeds may be advisable. Increases in screen brightness 
would call for greater operating speeds but, of course, there is a limit to acceptable 
film consumption. 

Furthermore, camera and projector exposure times have great influence on the 
smoothness of projection. The greater the exposure time in relation to the time of 
occultation, the smoother and more pleasing the projected image will appear. 

MR. GRIFFIN: Those who remember the projection of pictures back in the 
silent days will recall that pictures were not projected at 16 frames a second. 
They were projected more nearly at 18 or 20 frames a second and more. But 



Sept., 1940] QUALITY IN TELEVISION PICTURES 251 

under normal circumstances where good projection was required, it was decided 
by the Society that the projection of pictures at 16 frames a second was entirely 
too slow, and that the eye retained the impression of each succeeding picture. 
It was not solely on account of flicker, but because more frames per second were 
required to get the proper illusion of motion of a relatively fast-moving subject, 
that the projection speed was increased. So I should say that 30 to 40 frames per 
second now, if apparatus standards could be changed and the producers would be 
satisfied to use the amount of film required, would provide far superior projection 
to that obtained by present-day standards. 

MR. CRABTREE: Unless the televised pictures which we are going to see this 
evening are much better than what I have seen, there is no question in my mind 
that the definition is not good enough to get by, at the present time. As has been 
shown, it is theoretically possible with 441 lines to secure better definition than is 
now being obtained. 

What are the principal factors involved, and what must be done to achieve 
better definition with 441 lines? 

MR. DYER: It would take a long time to go into those questions. The receiv- 
ing tube is probably one of the most serious limiting factors. The scanning spot 
size and receiving tube are certainly two of the things that a person would attack 
first the spot size changes according to the brilliance. The spot size can be very 
small if operated at low brilliance, but if we try to obtain better picture quality by 
increasing the brilliance, the picture quality immediately will suffer by loss in 
definition. 

I do not know under what conditions the pictures you have seen have been 
shown; but in the home today, in many cases in large cities, reflections in the 
transmission path cause loss of detail having nothing to do with the television 
system, as such. That can be improved by modifying antennas and changing 
their locations. The transmitting equipment does not need to be as much of a 
factor in the loss of detail as the receiving equipment. 

DR. GOLDSMITH: As a practical proposition, when everything is working 
properly in the system, you can take a page of a newspaper, for example, the New 
York Times, and hold it in front of the camera to fill the field. In the home you 
can then read everything down to, but not including, the 6-point type. Every 
headline is readable. That represents fairly good definition in a picture only 
7 l /t by 10 inches. Mr. Crabtree has evidently been unfortunate in his experience 
in that regard because present-day television close-ups show very fine detail. 

MR. CRABTREE: I am speaking of what has been most recently demonstrated 
publicly by two of the larger manufacturers. 

MR. DYER: At one time in our studios we made prints of a subject on 8-mm, 
16-mm, and 35-mm film (the same print), and projected all three of these prints 
side by side on the screen, which was about 12 or 14 inches wide. Then we pro- 
jected a television image of the same picture, in the same size. We asked a group 
of non-engineers to look at the pictures and decide how good they were and where 
the television picture stood in relation to the others. Discounting brilliance, it 
was found that there was no question that the television picture was better than 
the 8-mm film, but that it was not as good as the 16-mm. The test was not indic- 
ative of the type of picture we showed here tonight, because the receiving tube 



252 P. C. GOLDMARK AND J. N. DYER [J. S. M. P. E. 

was not capable of producing anything like the definition of these idealized pic- 
tures. 

MR. BEDFORD : I would like to congratulate Mr. Dyer on effectively demon- 
strating that a satisfactory television picture can be reproduced with 441 lines 
when we learn how to do it. There is one point, however, of an academic sort, on 
which I would like to express a difference of opinion. He indicated, I believe, that 
if a picture were transmitted using a perfect storage device at the pick-up end of 
the system, and a perfect storage device at the receiving end of the system, even 
though the picture were transmitted at the rate of 15 frames a second, there would 
be neither jerkiness of motion nor flicker. If I understand correctly, what would 
happen is that the picture would be blurry due to the storage effect at the trans- 
mitter, but there would also be jerkiness because the blurry picture would be re- 
produced as a series of stills. So I believe we would have both jerkiness and blur 
in that case. If I should pick an ideal system, I believe it would be better to have 
an instantaneous pick-up device and complete storage at the receiver. 

MR. MAURER : A number of years ago I had occasion to work with an inventor 
who had devised a continuous projector and camera with which he could photo- 
graph at any speed he desired. With this camera he obtained a continuous record 
of everything that went on, subject to the blurring that would occur. In other 
words, there was no part of the cycle during which his lens was not making an 
image on the film. When he took pictures of athletes going through rapid motions 
and projected them with a similar continuous projector mechanism, the effect was 
generally smooth and surprisingly satisfactory, even at as low a speed as 10 frames 
a second. But when he used the same continuous projector with a picture that 
had been taken with the usual intermittent type of camera, where each image was 
sharp, as soon as the speed dropped below about 20 frames a second a certain 
jerkiness was noticeable, which became quite obvious at 16 frames a second. The 
transition or jump from one fixed stage of the motion into the next fixed stage was 
a great deal more objectionable, in my opinion, than the complete blur that oc- 
curred by having the image show everything that took place. 

DR. GOLDSMITH: The idealized type of projector which we are discussing 
is the non-intermittent constant-brightness projector. In this form of an "ideal" 
cinematic system, a camera which took a picture with the brightness of the picture 
constant on the film throughout the photographic cycle and a projector which 
projected the picture with constant brightness throughout the rectification cycle 
would be used. With such a combination, it is a fact that one can tolerate a lower 
number of frames per second, provided there is really constant-brightness non- 
intermittent projection, and provided that one is using a type of studio and pro- 
jector lighting that is difficult to define, but consistent with that mode of presenta- 
tion. 

On the other hand, I can not quite agree, from my own experience, that one can 
go down as low as 20 frames a second and get away from flicker on a bright pic- 
ture, for example, of a fencing match where there are brilliant and separated 
reflections on a rapidly moving foil. 

MR. MAURER: I agree with that. The action in the pictures I saw was run- 
ning, diving, and swimming. 

MR. FRIEDL: I am interested in Mr. Dyer's comment about the quality of the 
television picture as compared with 8-mm, 16-mm, and 35-mm film pictures. I 



Sept., 1940] QUALITY IN TELEVISION PICTURES 253 

heard the statement at a previous meeting, but not so broadly. The previous ref- 
erence was to the definition of the television image, as compared to the 8-mm 
and 16-mm. 

Inasmuch as a number of factors contribute to the "quality" of a picture, there 
was a question as to whether or not definition alone was being judged as a measure 
of quality. As a comparison of picture for picture on an overall quality basis, a 
specific question was asked; i. e., if you were to project an 8-mm or 16-mm film 
on a screen adjacent to and of the same size as a television image, would the tele- 
vision image be selected in preference to the 8-mm or 16-mm? 

The last time the question was raised, I believe it was answered by saying that 
it is comparable in definition only not in flatness of field, not in contrast, and not 
in brilliance. "Definition only" is a nice rule-of -thumb comparison to make, but 
I am afraid it will leave a lot of people expecting too much of television. I am an 
8-mm "fan," and I have yet to see a television image that compares with my 8-mm 
pictures. 

MR. DYER: The test I described was made by reducing the brilliance of the 
8-mm and other projectors to the brilliance of the television picture. If you accept 
that limitation the layman's answer seemed to be that he preferred the television 
image to the 8-mm. 

MR. FINN : Considering the experience the motion picture people have had, I 
think it ill becomes a group of men who must notice every day the wide vari- 
ance in density among reels of a given picture to criticize severely a new art for lack 
of detail. From my point of view I think the television images are fine; and when 
I see the change-overs in some of our de luxe picture houses, with all our past ex- 
perience, I am inclined to think they may be better. 

MR. BEERS: With regard to the comparison between the television image 
and that obtained from motion picture film, I believe I am the one who answered 
the question at the previous meeting. The reason why the comparison was made 
on the basis of definition only was that definition is the factor that is primarily 
determined by the standards we are using. Picture quality, contrast, etc., are 
characteristics on which we have sufficient information to know that we can con- 
trol them, and, in the future, improve them to the point where we feel they will be 
comparable with the results we get from film. 



A NEW METHOD OF SYNCHRONIZATION FOR 
TELEVISION SYSTEMS* 



T. T. GOLDSMITH, JR., R. L. CAMPBELL, AND S. W. STANTON** 

Summary. Line and frame scanning frequencies in an all-electronic television 
system need not be frozen to a standard giving limited definition performance if the 
synchronizing system is arranged so as to allow flexible operation. Automatic 
operation of receiver synchronizing circuits at variable line and frame frequencies is 
made possible with the aid of a new type of synchronizing wave-form. Synchronizing 
standards which permit both flexible and automatic operations are discussed. Trans- 
mitter synchronizing apparatus for flexible synchronizing standards, receiver cir- 
cuits for both non-automatic and automatic synchronizing operation are also dis- 
cussed, and 'a "transition" type receiver for operation on both old and new types of 
synchronizing signals is briefly described. 

While 441 -line television represents a good starting point for public 
service in a restricted experimental manner, it is quite likely that wide 
public acceptance will demand, among other things, increased defini- 
tion performance. With present-day screen projection as a standard 
of comparison, it appears certain that better definition is a "must" for 
television in the near future. To obtain pictures having better defini- 
tion it finally becomes necessary to add more scanning lines, which 
requires a change in either horizontal or vertical scanning frequencies, 
or both. A logical improvement, therefore, is a synchronizing system 
that will allow a television receiver to operate at various line and 
frame frequencies without requiring changes in circuit constants. 

Before proceeding to the subject in point, a brief outline of the 
principles of television synchronization will be in order. Present 
practice is to send the line and frame synchronizing pulses mixed 
with the video signals over a common channel. For line scanning a 
horizontal synchronizing pulse is transmitted during the flyback 
period of each scanning line, and a vertical synchronizing pulse is 
transmitted during the vertical flyback period. These two syn- 
chronizing signals are formed at the transmitter, and are first mixed 

* Presented at the 1940 Spring Meeting at Atlantic City, N. J.; received 
June 14, 1940. 

** Allen B. Du Mont Laboratories, Passiac, N. J. 

254 



NEW METHOD OF SYNCHRONIZATION 255 

together and then mixed with the video signal to form a composite 
television signal. At the receiver it is necessary first to separate the 
synchronizing signal from the video, and then segregate the horizontal 
and vertical synchronizing components from the separated syn- 
chornizing signal. A television channel therefore has three dis- 
tinctly separate signals which must be transmitted simultaneously 
without interaction and then utilized separately at the receiver. 

It is possible, of course, to permit some interaction and consequent 
imperfections in synchronizing signals by employing weak syn- 
chronism at the receiver. Weak synchronism, however, is not desir- 
able in a flexible system because of the necessity of having synchroniz- 
ing controls at the receiver. These controls are usually a fine fre- 
quency adjustment on the sweep oscillators, and unless synchroniz- 
ing action is very positive, they are in need of adjustment frequently. 

If the synchronizing signal is such that it will permit positive 
synchronism without distortion effects due to incomplete isolation, 
the synchronizing controls at the receiver can be eliminated. A 
further step is to do away with the self-oscillating feature of the 
sweep circuits, so that the frequency of receiver scanning is entirely 
dependent upon the synchronizing signal being transmitted. This 
latter step is called "automatic synchronization." In a strict sense, 
the term "automatic synchronization" is applied to receiver circuits 
wherein there is no scanning action unless the synchronizing signal is 
being received. However, it is possible, with proper synchronizing 
signals and choice of circuit constants, to operate self-oscillating 
sweeps so that they will remain synchronized over a reasonable range 
of scanning frequencies. 

AUTOMATIC SYNCHRONIZATION 

Automatic synchronization, however, provides for flexibility as 
well as positive synchronism because the circuits used at the re- 
ceiver need not be of the self -oscillating type. This simplifies the 
control-panel problem for the lay-user in that there is no perplexing 
disintegration of the picture due to the loss of synchronism such as 
in the self-oscillating type of circuit when the sweep-frequency con- 
trols are out of adjustment. 

In the self -oscillating type of sweep circuit the oscillator is tripped 
by the incoming synchronizing pulse, which times the discharge of 
the oscillator used to control the discharge tube. Because of the 
blocking action of the oscillator, it is. non-receptive to incoming 



256 



GOLDSMITH, CAMPBELL, AND STANTON [J. S, M. P. E. 



signals except in the region of the firing interval. This phenomenon 
should be- kept in mind, for in it lies the main advantage of an oscilla- 
tor as a means of initiating sweep discharges. 

The usable portion of the oscillator discharge pulse that is used 
to control the discharge tube resembles closely the shape of the trans- 
mitted synchronizing pulse. It is thus seen that the oscillator por- 
tion of a self-oscillating sweep circuit serves as a combination buffer 
and filter circuit. This buffer action has been necessary for two 
reasons, viz., 



OK/Z. Syc. 



j-y/vc. 
JCf-'AKArof 
crocus rj 



wn 




m 

UUP 

FIG. 1. Basic automatic synchronizing circuits. 



(1) Imperfections in the received synchronizing signals, these being due to: 

(a) Incomplete isolation of horizontal and vertical synchronizing 
signals, and/or distortions in the isolated signals introduced by 
the isolating networks. 

(6) Incomplete removal of the video component from the synchroniz- 
ing signal. 

(2) Nullification of noise disturbances between synchronizing intervals, 

due to the well known blocking effect. 



In Fig. 1 is shown a circuit for automatic synchronization of re- 
ceiver scanning. The circuit is essentially the same as is used for 
self-oscillating sweeps from which the oscillator circuits have been 
removed. Vertical and horizontal synchronizing pulses, having 
been isolated in the synchronizing separator, are applied to their 
respective saw-tooth generators directly. A proper choice of time 
constants in the discharge circuits provides for a sufficiently linear 
saw-tooth output over a satisfactory range of scanning frequencies 
It will be seen that the output voltage of the discharge circuits wil 



Sept., 1940] 



NEW METHOD OF SYNCHRONIZATION 



257 



vary inversely with the frequency of the applied synchronizing pulse. 
A gain adjustment, either of the manual or automatic variety, must 
be provided to hold the required scanning amplitude over the de- 
sired range of frequencies. This change in amplitude is not con- 
sidered a disadvantage, however, since the picture remains syn- 
chronized, and it becomes quite simple for the user to diagnose the 
difficulty. In fact, self-oscillating circuits require the same ampli- 
tude control, as well as a frequency adjustment if they are to be 
flexible. 




fa.) 




V0LT/lff. 



FIG. 2. Synchronizing and oscillator wave-forms. 

The effects of noise upon these circuits is explained by means of 
Fig. 2. Assuming that the discharge tube is biased so that it is 
actuated by as much of the incoming synchronizing wave as is 
feasible, Fig. 2(a) shows that a pulse of noise (the dotted portion) 
will cause the circuit to fire prematurely and mistiming of discharge 
will result. In Fig. 2(c) is shown the wave-form typical of the 
blocking oscillator circuit, while Fig. 2(d) shows the synchronizing 
wave-form applied to the oscillator circuit. The highly negative 
signal occurring immediately after discharge acts to block the circuit 
for a considerable portion of the period before the occurrence of the 



258 GOLDSMITH, CAMPBELL, AND STANTON [J. S. M. p. E. 

next pulse. By means of an inverse feedback circuit it is possible 
to cause blocking in a similar fashion in an automatic sweep circuit. 
Thus the automatic type of sweep circuit can be made to have noise 
characteristics substantially identical with those of the self -oscillating 
type of circuit. 

SYNCHRONIZING SIGNALS FOR AUTOMATIC SYNCHRONIZATION 

Automatic synchronization can be accomplished only with good 
isolation of synchronizing pulses at the receiver. It follows, there- 
fore, that the synchronizing signal transmitted should be of such 
character that it can readily be broken down into horizontal and 
vertical signal components, each independent of the other although 
they have been transmitted as a composite synchronizing wave. 

The isolated horizontal synchronizing pulses must be a continuous 
wave-train of homogeneous pulses entirely free from any low-fre- 
quency component in the region of the vertical pulse interval for 
best performance conditions of automatic horizontal synchronization. 

Automatic synchronization of the vertical sweep circuit is even 
more complex in that not only must a pulse be separated entirely 
clear of the horizontal pulses in order to insure proper interlace at 
the receiver, but it must be free from low-frequency variations such 
as line surges, etc. This operation is further complicated when the 
vertical synchronizing pulse is designed to have a minimum effect 
upon the horizontal synchronizing signals. 

Since automatic synchronization utilizes nearly all the synchro- 
nizing information that is transmitted, it can be seen that the signal 
applied to the respective circuits must be of good quality. This 
means that the video component must also be well separated from 
the synchronizing signal. Amplitude separation as a means for 
removal of the synchronizing component from the video component 
has been found to work satisfactorily for automatic synchronizing 
receiver operation. Care must be exercised, however, in the design 
of the amplitude-selective networks in order to maintain adequate 
separation over a reasonable range of total signal level. 

A brief discussion of some of the synchronizing wave-forms em- 
ployed in the past will enable a clearer understanding of the dis- 
cussion to follow. 

In Fig. 3, some of the more commonly known types of synchroniz- 
ing wave-forms that have been in use at some time or other in the 
past are shown. 



Sept., 1940J NEW METHOD OF SYNCHRONIZATION 259 

Wave-form a shows a form of amplitude selection for vertical 
synchronizing which was first advocated by Vance, a modification 
(dotted wave) of this being later proposed by Philco. The chief 
disadvantage here is that a separate amplitude level must be main- 
tained for the vertical synchronizing pulse, and it is therefore waste- 
ful of transmitter power. Furthermore, the vertical pulse interval 
is considered to be too short for satisfactory operation. 

Wave-form b shows the type of pulse that was used to overcome 
the difficulties previously encountered with a, and here the difficulty 
is introduction of distortion in the horizontal synchronizing wave- 
train in order effectively to transmit the vertical. With this type 
of pulse, the so-called "flywheel" action of the sweep oscillators was 



JLJ1 fUUUUUVWWIA A. 

9 

'JUUUWWU 

FIG. 3. Experimental synchronizing wave-forms. 

utilized to keep the horizontal circuit in operation during the ver- 
tical pulse interval. This method of operation was unsatisfactory, 
however, in that horizontal synchronizing stability was extremely 
poor. 

Wave-form c shows a means of transmitting continuous horizontal 
synchronizing by means of a chopped or serrated vertical pulse. 
Also here is shown the introduction of the equalizing pulses along 
with the vertical pulse for the purpose of improving the interlacing 
characteristics. This type of wave gave distortion of the horizontal 
synchronizing pulses during the vertical pulse interval due to the 
presence of high-frequency components in the vertical pulse. 

Wave-form d (Fig. 3) shows a method similar to c, except that an 
amplitude separation is employed in order to obtain continuous 
horizontal synchronizing. This has practically the same disad- 



260 



GOLDSMITH, CAMPBELL, AND STANTON [J. s. M. P. E. 



vantage as a, and it is considered a workable system. Two methods 
of selection are employed as a means of isolating the two signals, 
amplitude for the horizontal, and frequency selection for the vertical. 
Now, in wave-form e a method is shown for obtaining continuous 
horizontal synchronizing without resorting to amplitude means. 
This is probably the most effective attack to the synchronizing 
problem up to this time, and is due to Percival and Browne of E. M. I. 
Continuous horizontal synchronizing may be obtained by utilizing 
the steepness of wave-front of the sections of vertical pulse. 



-L 





FIG. 4. Du Mont synchronizing wave-forms. 

The RMA type Till pulse is shown in wave-form / (Fig. 3), and 
it will be seen that this is a combination of the E. M. I. Marconi 
standard (wave-form g) plus the equalizing pulses shown in c. 

The RMA type of pulse, however, does not lend itself readily to 
adaptation to automatic synchronizing circuits. While it is possible 
to obtain a continuous horizontal synchronizing signal from this 
type of wave, the presence of equalizing pulses, plus the low-frequency 
components during the vertical pulse interval, does not provide a 
pure horizontal synchronizing wave-train such as is desirable. The 
resulting unwanted low-frequency components cause transients in 



Sept., 1940] 



NEW METHOD OF SYNCHRONIZATION 



261 



the horizontal circuit when it is being driven, which give rise to 
distortion of the scanning pattern at the top of the picture. Isola- 
tion of the vertical synchronizing to a degree where it is possible to 
utilize the pulse to drive automatic circuits is accomplished only 
with considerable difficulty. 

The type of synchronizing wave found to be most satisfactory for 
automatic synchronizing purposes is shown in Fig. 4. The vertical 
pulse is transmitted in a series of high-frequency pulses which are 
mixed with continuous horizontal synchronizing for transmission, 
and subsequently separated at the receiver by simple filter circuits. 

This form of synchronizing signal has been found to have decided 
advantages when it comes to isolating the two components at the 




FIG. 5. Synchronizing generator for Du Mont synchronizing. 

receiver. The vertical synchronizing signal is eliminated from the 
signal applied to the horizontal circuit by means of a wave-trap. 
This selective circuit is used to isolate the vertical synchronizing 
signal which then may be applied to the vertical sweep circuit either 
directly as a radio -frequency signal or detected and subsequently 
applied to the circuit. 

The production of this type of synchronizing wave is quite simple 
when compared with formerly used systems. Fig. 5 is a block 
diagram of synchronizing pulse-forming circuits. To obtain the 
vertical pulse, the carrier-frequency is first developed in a frequency 
multiplier circuit. This produces a carrier a, harmonically related 
to the horizontal synchronizing frequency, which is an important 
factor as will be shown later. The carrier is then electronically keyed 



262 



GOLDSMITH, CAMPBELL, AND ST ANTON [j. s. M. P. E. 



by means of pulse b during the vertical pulse interval, the resulting 
signal being as indicated in the figure at c. 

This signal is then mixed with the horizontal synchronizing wave- 
train d, which results in the signal shown at e. Next, the lower 
part of the vertical pulse envelope is "clipped" off (/), so that the 
resulting vertical synchronizing wave is a series of rectified pulses at 
the carrier-frequency. This latter operation is necessary in order to 
prevent the lower half of the envelope from extending beyond the 





Composite synchronizing signal. 



Complete elimination of verti- 
cal pulse. 





Partial elimination of vertical pulse. 

FIG. 6. Oscillograms of isolated synchronizing wave-forms. 



Vertical pulse free of horizontal 
pulses. 



picture "black level." It will be seen that an added component is 
obtained during the horizontal pulse interval, and, also, the negative 
portion of the vertical synchronizing carrier cycle subtracts from 
the horizontal pulse. The additive components may be "clipped" 
or "saturated off" without detrimental effects to the synchronizing 
performance. The resulting wave-form is as shown at g (Fig. 5). 
Upon removal of the 530-kilocycle component from the synchroniz- 
ing signal the. horizontal pulses are restored substantially to their 
original shape, and thus the resulting horizontal wave-train is con- 
tinuous. 



Sept., 1940] NEW METHOD OF SYNCHRONIZATION 263 

RECEIVER CIRCUITS FOR AUTOMATIC SYNCHRONIZATION 

In Fig. 6 are shown oscillograms of the composite synchronizing 
signal as received, and the two separated components. It will be 
noted that the horizontal synchronizing pulse is entirely free of the 
vertical pulse, and the isolated vertical wave is devoid of horizontal 
synchronizing. Fig. 7 shows the frequency characteristics of the 
circuits used for horizontal and vertical synchronizing selection. 

The isolated vertical synchronizing pulse is sufficiently free of 
unwanted disturbances so that it may be used to trigger a rather 




FIG. 7. Synchronizing selector network characteristics. 

simple form of sweep system. Fig. 8 shows a "gas discharge" type 
of saw-tooth generator that operates quite satisfactorily. The 
gas tube is operated with a negative cut-off bias so that the circuit 
fires only when radio -frequency signals are applied to the grid. The 
saw-tooth output from the plate circuit is independent of input 
signal variations in amplitude or wave-form. 

A schematic diagram of the receiver sweep circuit using automatic 
synchronization circuits is shown in Fig. 9. Both vertical and hori- 
zontal sweep circuits are of the non-oscillating type, and conse- 
quently will follow any frame or line frequencies that it is desirable 
to transmit. 



264 



GOLDSMITH, CAMPBELL, AND STANTON [J. s. M. p. E. 



Under no signal condition, there is no scanning voltage generated, 
and therefore it is necessary to remove the spot from the screen to 
prevent burning. There are several methods for accomplishing this 
protection, and at present it will suffice to say that the absence of 
scanning signals operates a device that prevents the electrons from 
reaching the fluorescent screen. 

For noise-free operation this system uses the principle of blocking 
previously explained, together with a limiting device that prevents 
the noise from exceeding a predetermined amplitude. 

Generally speaking, the horizontal synchronizing channel is more 
susceptible to noise effects, and anti-noise precautions are necessary 
in order to operate at locations where the noise level is high. Be- 
cause of the comparatively narrow band employed for the vertical 
pulse, the noise problem has not been found to be serious in this 



-1-11- <- 

JAW roar* 
oum/r 

L- /* 




FIG. 8. Synchronizing circuit using gas triode. 

channel. There are, however, several worth-while anti-noise cir- 
cuits that could readily be applied to the vertical synchronizing 
channel. 



RECEIVER CIRCUITS FOR BOTH AUTOMATIC AND NON-AUTOMATIC 
SYNCHRONIZING SIGNALS 

In the foregoing a completely flexible and automatic system of 
synchronization has been described. In order to utilize transmis- 
sions operating at the present time on non-flexible standards, as 
well as future transmissions at improved standards, a "transition" 
type of receiver becomes necessary. The synchronizing circuits 
for such a receiver are shown in Fig. 10. With a receiver of this 
type, semi-automatic synchronization can be employed and still 
provide satisfactory operation on both old and new types of synchro- 
nizing signals. 

During the time when some stations are transmitting the RMA 



Sept., 1940] 



NEW METHOD OF SYNCHRONIZATION 



265 



type of synchronizing signal and others are transmitting the radio - 
frequency vertical pulse synchronizing signal, it is going to be neces- 
sary to provide receivers with local oscillators and separator circuits 
capable of utilizing either type of pulse. Eventually universal 
adoption of the new synchronizing signal will enable receiver manu- 
facturers to make full use of the advantages of the Du Mont signal 
with an entirely automatic set of sweep circuits. In the transition 
set there is still need of sweep adjustments for sweep speed, and as 
a practical circuit a two -position switch chooses either of two groups 




FIG. 9. Automatic synchronizing receiver circuits. 



of potentiometers which can be set independently of each other, say, 
for 441 lines, 30 frames, and for 625 lines, 15 frames. 

Satisfactory, though not the most efficient, circuits are available 
to use either RMA or Du Mont synchronizing pulses without switch- 
ing except for sweep speeds. However, when all transmitters 
eventually use the radio-frequency vertical pulse type of signal, 
the proper tuned circuits for maximum selectivity of the 500 kilo- 
cycles vertical information will yield superior stability, and interlace 
then can be obtained in the temporary transition type of receiver. 



266 



GOLDSMITH, CAMBPELL, AND STANTON [J. S. M. p. E. 
CONCLUSION 



The tests of this synchronizing signal show that it is thoroughly 
adequate for flexible operation. However, it is quite apparent that 
other components of the transmitting and receiving systems today 
limit the definition that can actually be achieved. Nevertheless, 
as the other components are improved, with such a system in opera- 
tion as described above, the much-needed improvement in definition 
can be achieved gradually without necessity of complete replacement 
of equipment. 




VIDEO AMPLIFIER 



HORIZONTAL SEPARATOR 




SWITCH FOR 3PEEO AND 
SIZE CONTROLS TO 
OBTAIN TWO PRE-3ET 
FREQUENCIES- e.g. 
441-30 AND CZ5-I5 



FIG. 10. Semi-automatic synchronizing receiver circuits. 



The radio-frequency pulse type of synchronizing signal described 
above would seem to possess the following advantages over pre- 
viously described methods of transmitting the synchronizing in- 
formation : 



(1) Ease of generation at the transmitter. 

(2) Ease of separation at the receiver. 

(5) Adaptability for use with simple "automatically synchronized" receivers, 
permitting reception from "high-definition" stations as well as "low- 
definition" stations, without the necessity of a service-man to readjust 
synchronizing and speed controls, and, more important, permitting in- 
creases in vertical definition as the art advances without necessitating 
replacement or modification of receiving equipment. 



Sept., 1940] NEW METHOD OF SYNCHRONIZATION 267 

BIBLIOGRAPHY 

WILSON, J. C.: "Television Engineering," Pitman & Sons (London), 1937. 

ENGSTROM, E. W.: "An Experimental Television System, Part I," Proc. 
IRE, 22 (Nov., 1934), p. 1241. 

KELL, BEDFORD, AND TRAINER: "An Experimental Television System, 
Part II," Proc. IRE, 22 (Nov., 1934), p. 1246. 

KELL, BEDFORD, AND TRAINER: "Scanning Sequence and Repetition Rate of 
Television Images," Proc. IRE, 24 (Apr., 1936), p. 559. 

FINK, D. G.: "Principles of Television Engineering," McGraw-Hill Book 
Co. (New York), 1940. 

CAMPBELL, R. L.: "Television Control Equipment for Film Transmission," 
J. Soc. Mot. Pict. Eng., XXXIII (Dec., 1939), p. 677. 

ZWORYKIN AND MORTON: "Television," John Wiley & Sons (New York), 1940. 



REMOTE CONTROL TELEVISION LIGHTING* 
W. C. EDDY** 



Summary. The remote control lighting system now in use in the television 
studios of the National Broadcasting Company presents a completely new approach 
to the studio lighting problem. 

A new series of overhead units, mounting inside-silvered incandescent lamps, com- 
prises the foundation lighting equipment which can be controlled in rotation, tilt, and 
elevation from an operating platform. 

Flexibility has been incorporated to allow the lighting engineer to arrange the 
lighting to his satisfaction and to change the lighting completely without interrupting 
the program. 

The units themselves have been designed around the specific requirements of the tele- 
vision cameras, and show under test a satisfactory efficiency both as to power consump- 
tion and dissipation of heat. The weight, of the order of 13 pounds per kilowatt, 
coupled with the extreme flexibility incorporated into the mechanical arrangement, 
appears to have solved the physical problem of installation. 

Lighting personnel requirements are substantially reduced, and with the major part 
of the installation now attached to the overhead gridiron, additional valuable floor space 
has been given over to the cameras. 

Illumination levels as high as 2400 foot-candles can be created on an average set, but 
due to general improvement of both camera tube and circuits, it is seldom necessary to 
exceed 800 foot-candles in foundation light. 

Combining flexibility with economy of operation it appears that this new lighting 
system has solved many of the problems of illumination in a television studio. 

In view of the experience so far obtained from our experimental 
television program service, it is now possible to analyze critically the 
lighting equipment used in the television studios of the National 
Broadcasting Company at Radio City. This equipment, while con- 
sidered by some to be radical in design, is the result of steady develop- 
mental work initiated during the RCA television field test in 1935. 
At that time it was apparent that a television stage would require an 
unusually high level of illumination, but beyond that we were left to 
guess the trend that television program technic would take and the 

* Presented at the 1940 Spring Meeting at Atlantic City, N. J. ; received April 
20, 1940. 

** National Broadcasting Company, New York, N. Y. 

268 



REMOTE CONTROL TELEVISION LIGHTING 269 

demands that it would make on our lighting equipment. It was to be 
expected then that our original lighting installation should be similar 
to that used on the smaller Hollywood sets. This equipment did 
produce illumination which at the time was considered satisfactory, 
but with the advent of multiple stages it was apparent that lighting 
was one of the problems which would seriously complicate the advance 
of program work if continued along these lines, because television had 
developed a technic entirely different from that used in motion pic- 
tures. 




FIG. 1. A stage set-up in the television studio. 

Specifically, our original equipment consisted of the usual array of 
focusing spots, scoops, broadsides, and rifles, all floor-mounted and 
all taking up floor space which should have been allotted to camera 
movement (Fig. 1). With the increase in size of the sets came an in- 
crease in the equipment and personnel required for operation, all of 
which further cramped the proper movement of the cameras. It was 
more to relieve the congestion and reduce the active personnel on the 
floor than to improve the lighting that a rearrangement of this equip- 
ment was undertaken. Installation of a portion of the units on a 
gridiron overhead was our first alternative, but the steady demand 
for still bigger sets requiring more light soon led us into an arrange- 
ment of fixed-focus lens lights arranged in a semi-hemisphere over an 



270 



W. C. EDDY 



Lr. S. M. p. E. 



area providing for a single set (Fig. 2). This addition, creating as it 
did a diffused foundation light of approximately 1000 foot-candles on 
all portions of the set, allowed us to utilize the focusing portable equip- 
ment for modeling and effect work, but such a fixed array did limit 
the program possibilities to a single set. The ever-increasing pro- 
gram demands for a multiple-set studio indicated that we had not yet 
evolved a satisfactory answer to the lighting problem. The equip- 
ment then in use to illuminate the single set was taxing the power in- 
put to the studio, so our attention was turned to the design of a more 
efficient lighting system rather than additions to the already hetero- 
geneous assortment already acquired. 




FIG. 2. Illumination by battery of 500-watt units. 



The inside-silvered incandescent lamp proved to be a logical start- 
ing point and an experimental installation of six lamps was designed 
and installed in the Radio City studio. A substantial gain in useful 
light for a given amount of power was immediately apparent, and 
steps were taken to substitute units of this type for the original equip- 
ment. The constructional data on these units have already been pre- 
sented before the Society 1 and we shall therefore limit our description 
to a pictorial review. 

Our original unit, called the "single six" (Fig. 3), was composed of 
six 500-watt bulbs mounted in line on an adjustable arm. This 
equipment produces at a distance of four feet or greater a sheet of 



Sept., 1940] REMOTE CONTROL TELEVISION LIGHTING 271 

diffused light, satisfactory in spectral quality for the television 
camera. 

The "double three" (Fig. 4), a modification of the "single six," was 
found to be adaptable in the studio both as to maneuverability and 
the characteristics of the light-beam produced. 

The "single three" (Fig. 5), one-half of the standardized "double 
three," is mounted vertically on an adjustable floor stand and is 
utilized for strip lighting and background illumination. In this case 
the narrow sheet of light works to our advantage in illuminating back- 
grounds without endangering the foreground modeling. 




FIG. 3. The single-six mounting. 

The "double three," less its supporting arm and mounted on a port- 
able floor-stand, becomes the equivalent of the broadside, producing 
three kilowatts of directed, diffused light in a rectangular pattern 
(Fig. 6). Two of these units are normally used in any television 
production, the major part of the modeling or cross-lighting on the 
set being accomplished with these lights. 

A "single three" mounted horizontally on the remotely controlled 
pedestal becomes the portable footlight (Fig. 7) which is brought into 
play in sequences demanding such illumination. In this case the 
operator remains well behind the camera and manipulates the lights 
with controls brought out to the operating handle. 



272 



W. C. EDDY 



tf. S. M. P. E. 



Overhead at either end of the studio we have two master modeling 
units (Fig. 8) which can be swung through 360 degrees and tilted 
through 180 degrees. These units are the largest in the studio and 
can be considered as all-purpose lights, although their specific duty is, 
as their name implies, to establish the modeling angle of the light on 
the set. 

The basic light of the entire installation is of course the remotely 
controlled "double three" (Fig. 9), of which type we have twenty- three 
installed on the gridiron in the studio. Before going into the details 

of this unit, let us take up the 
story chronologically in order 
better to bring out the need for 
such a device. 

Observation of the studio tem- 
perature and lighting loads in the 
early stages of our adoption of 
inside reflector lamps confirmed 
our assumptions as to the choice 
of this light-source. We at last 
had light available for the larger 
and more complicated sets de- 
manded by program require- 
ments, with neither the electrical 
load nor the studio ambient tem- 
perature registering a marked 
increase over the average opera- 
tional mean of previous months. 
We were able to produce more 

light with less power. We were able to direct our light manu- 
ally on more than one set, even though such a change did require 
time and personnel. The ambient heat problem had been reduced to 
a more reasonable ratio of the light used to the heat dissipated in the 
studio and furthermore, with the flexibility now given the lighting 
engineer, the overall lighting of the sets was beginning to show im- 
provement. We were, however, still forced to introduce a film inter- 
lude or intermission between sequences to allow the personnel to re- 
adjust the lights, a complication that still limited the efforts of the 
programming staff and required considerable lighting personnel in the 
studio. We had the alternative, of course, of installing sufficient 
equipment overhead to illuminate each set individually, but such a 




FIG. 4. The double-three unit. 



Sept., 1940] REMOTE CONTROL TELEVISION LIGHTING 



273 



move was impracticable for several reasons. First of all, where a suc- 
cession of sets is being used to shoot a television program it is gen- 
erally necessary that these sets adjoin or overlap each other, so that 
the sets can be quickly and quietly shifted during the few seconds of 
the opening lines. Such an arrangement predicates a series of sets 
opening on a central shooting or camera area, and, of course, also 
predicates a common ceiling facing all sets. It would therefore be 




FIG. 5. 



The single-three 
unit. 



FIG. 6. The floor broad. 



impossible to install the equipment required by reason of these space 
limitations. In addition, although this particular studio had a spe- 
cially reinforced ceiling designed to carry a reasonably heavy hanging 
load, a radical and major redesign would be required to carry the 
additional load of a duplicate lighting system. If further proof were 
needed that our one solution lay in increasing the flexibility of the 
present layout, it was found in the unavailability of the necessary 
power to energize new equipment. 

We therefore designed and constructed an experimental "double- 
three" unit controllable in rotation, tilt, and elevation by means of. a 



274 W. C. EDDY [j. s. M. P. E. 

series of ropes. This device was successfully tested in a studio pro- 
gram early in the summer of 1938 and because of its apparent possi- 
bilities for studio work, it was redesigned for production. 

This "flexible double three" has become the basic unit of our re- 
motely controlled lighting system. It consists of a standard fixture 
mounted on a hollow arm through which cables pass to rotate, tilt, 
and elevate the assembly. With a series of these remotely controlled 
units mounted overhead on the gridiron, their hemispheres of opera- 
tion tangent to each other (Fig. 10), it is possible to select the particu- 
lar lights available to any stage. The remaining units can then be 
reset remotely for the next sequence while the first group, when clear, 
can be brought into play on set three. This one-man control of the 




FIG. 7. Portable footlight. 

overhead or foundation lighting appeared to be one logical answer to 
television's requirement for extreme flexibility. By operating the 
available fixtures an operator can readily establish a modeling angle, 
can control and shift the back lighting as the characters move about 
the stage, and also can preset the scene to be televised next. In 
addition, the lighting engineer is also given the opportunity to vary 
the lighting while action is taking place on the set to satisfy either 
technical or program requirements. 

At the present time all control of these flexible units is accomplished 
by means of the four cables connecting each unit with the light-con- 
trol bridge in the rear of the studio (Fig. 11). This is the control 
center of the entire lighting installation and as such merits a more 
complete description. The bridge platform is elevated ten feet above 
the floor and flanked on two sides with studio walls on which are ar- 
ranged the fair-leads and cleats of the overhead array (Fig. 12). 



Sept., 1940] REMOTE CONTROL TELEVISION LIGHTING 



275 




>. 

"3 
o 

OJ 

^ 

OS 

6 
fe 



276 



W. C. EDDY 



[J. S. M. P. E. 




FIG. 10. ( Upper} Set of remotely controlled units, with hemispheres of 

operation tangent to each other. 
FIG. 11. (Lower) Light-control bridge. 



Sept., 1940] REMOTE CONTROL TELEVISION LIGHTING 



277 



Along the open side of the bridge overlooking the studio floor is the 
pin-rail and access ladder. An electrical control board carries the 
silent mercury tumbler switches and the cross-over knife switches of 
the master modeling units. Two-way phone communication is pro- 
vided between video control and the lighting engineer. But during a 
program this line is, of necessity, kept one way, light and hand signals 
being utilized in acknowledgments and in issuing instructions to the 
lighting technicians on the floor. 



Sfflllulnlrl 

I ill iliilklllllMliti'li 

j 31 1 13 H ; n i n 




FIG. 12. Close-up of bridge, showing fair-leads and cleats of the overhead 

lighting array. 

From the light-control bridge, the lighting engineer is able to view 
the entire studio. He can analyze the illumination on each stage and 
preset the succeeding stage while the action is going on in another 
part of the studio. Rearrangement of light can be and is continually 
varied to meet the requirements of the camera work. Movement of 
the two floor units is supervised and controlled by a system of hand sig- 
nals, attention of the operator being attracted by flashing one of the 
units not in use. 

With the full control of all the lights in the studio at his fingertips, 



278 W. C. EDDY [j. s. M. P. E. 

it is possible for the lighting engineer to create any reasonable lighting 
effect and illuminate any set satisfactorily for the television cameras. 
This, however, is nothing more than could be accomplished with a 
non-flexible system that had given way to the new installation. The 
test of this installation comes with the program utilizing a series of 
separated stages with little or no interval between sequences. In the 
cameras' operation, this requires only that one of the three cameras 
be withdrawn early enough in the closing sequence to be in position to 
open the new set. Audio can carry this change with a planted micro- 
phone for the opening lines until the boom can be swung around and 
faded in, but from the lighting angle such a change requires carefully 
timed maneuvering of the equipment to insure normal brilliance on 
the opening shot and no depreciation in light on the closing lines of the 
first set. In such a situation we make use of two suspended 6-kw 
broad units positioned at either end of the studio and controlled from 
the bridge separately from the other overhead array. These two 
units are termed master modeling units, from their normal use, but 
have proved invaluable in holding up the illumination during change 
of sets. 

It is impossible, of course, to lay down set rules for shifting lights 
during a multi-set show. With the script before him and cognizant 
of the positions of the cameras on the floor, the engineer will first 
swing all the available unlighted units into position over the set 
coming up. By watching the camera operation, he can then begin to 
rob the outside units on the working set and swing them onto the next 
stage. If it is necessary to reduce the overhead array by an extreme 
amount, the operators on the floor units are instructed to move in to 
cover. The master modeling unit is next swung into position over the 
working set and one or more of the floor units are drawn back and re- 
directed. Strip and ground row lighting has of course been planted 
during the early part of the sequence, so with the addition of the 
floor broads, the lighting can be considered normal and a verbal check 
is obtained from control on previewing the opening shot. As the ac- 
tion develops, more units from the first set can be brought over to re- 
inforce this second set, the remainder being swung to the third stage 
and the procedure repeated. 

Such a system of control necessitates only one and one-half to two 
times the equipment required to light a single set, but with proper 
manipulation any number of stages can be successively illuminated 
with similar, installations. 



Sept., 1940] REMOTE CONTROL TELEVISION LIGHTING 279 

In staging a variety show where the successive acts are rehearsed 
separately and no sequential plan of operation can be worked out, it is 
sometimes necessary to swing several banks of light simultaneously 
during the few seconds allotted to the Master of Ceremony's introduc- 
tion. To do this, the units affected are tied off separately and the 
control lines equipped with preset rings. At the conclusion of the 
act, these presets are released from their hooks and the entire over- 
head system drops to its new position on the next stage. 

To analyze our lighting installation, it is necessary to appreciate 
the difference between a television program and the shooting of a 
movie sequence. First, and of primary importance, is the fact that 
in television we have no editing privileges other than in the few 
seconds of preview obtained while focusing the opening camera. 
Second, our sets, of necessity, are adjacent to each other; and third, 
the restricted floor space must be kept clear for camera operation. 
This precludes any complication of floor-mounted equipment or extra 
personnel. 

Because of the proximity of the sets, the ceiling space before the 
various stages is common to each, and as has already been pointed 
out, the lighting equipment placed overhead must be common to all. 
A flexible system such as ours appears to be one solution. The plac- 
ing of all light-controls within the grasp of the lighting engineer allows 
him not only to exercise his own judgment in illuminating the sets, 
but in addition gives him an opportunity to correct an opening error 
without losing the entire sequence. This centralization of controls 
necessarily does away with the personnel required to handle the thirty- 
odd units that comprise the equipment. But by giving the engineer 
equipment that will satisfactorily produce a good television picture, 
and providing him with positive control of each unit wherever it may 
be positioned, it has, we believe, answered most of the present prob- 
lems in television lighting. 

To recapitulate, we have found that the remotely controlled founda- 
tion lighting possesses the required characteristics of extreme flexi- 
bility and high efficiency. The floor units are light, portable, and, 
where required, can be remotely controlled. The angle of overhead 
illumination can be adjusted and maintained for all conditions of set 
depth and length of throw. Backlight can be controlled remotely 
and can be made to follow the action on the stage. The problem of 
lighting successive stages can be handled either by splitting the avail- 
able light or by following the action directly with one or more banks 



280 W. C. EDDY [J. S. M. P. E. 

of the remotely controlled lamps. Economically the system now in 
use is satisfactory. With standard long-life lamps the replacement 
cost is quite low. The personnel requirements have been substan- 
tially reduced. At the present time three operators can satisfactorily 
handle all the lighting equipment even though an hour's program may 
cover as many as ten different stages. The set-up time formerly re- 
quired to readjust the studio lighting for a change in set location has 
been reduced from hours to minutes. Equipment has been simpli- 
fied, reduced in size, or removed from the floor altogether, providing 
additional space for camera operation. With one standardized type 
of light it is possible to estimate quickly the quantity of light and its 
distribution on the set rather than having to interpolate the resultant 
light from several different sources. 

Without attempting to give the impression that we have discovered 
the panacea of the lighting troubles in television, we do feel this in- 
stallation is a reasonable solution to our present requirements. This 
installation is but another phase of our developmental work in tele- 
vision. It is, we believe, a step toward solution of the problems of 
large-scale television broadcasting. 

REFERENCE 

1 EDDY, W. C.: "Television Lighting," /. Soc. Mot. Pict. Eng., XXXIII (July, 
1939), p. 41. 

DISCUSSION 

MR. KURLANDER: New York City has an ordinance requiring that the spot- 
light lenses be covered with wire netting. 

MR. EDDY: This unit has been approved by the New York Board of Fire 
Underwriters for all conditions of operation and fire protection. The lamps use 
300 watts apiece, making a total of 1 1 / 2 kw for the unit. With the 500-watt lamps, 
we use 3 kw. In two years of operation, during which we used something around 
86 kw nearly every day and most of the night, nothing has ever happened to the 
lamps. 

MR. KURLANDER : What is the average wattage on the set? 

MR. EDDY: We think in terms of foot-candles. We can not consider any one 
set, because the lighting depends upon the subject matter and the way in which we 
feel it should be lighted. One type of scene will be in a lower key than another. 
We use from 400 to 1000 foot-candles, 1000 being the maximum. 

MR. KURLANDER: The question of breakage is very serious. We have had 
some sad experiences with lamps that we thought were perfectly safe. When the 
filament of a gas-filled lamp operating at a high temperature fails in service, hot 
tungsten may drop on the bulb and create such severe glass strain that the bulb 
may explode. What protective measures have you for that? 



Sept., 1940] REMOTE CONTROL TELEVISION LIGHTING 281 

MR. EDDY: All these lamps are given a very thorough high- voltage test before 
being put into use. 

MR. KURLANDER : Does that mean that they will never burn out? 

MR. EDDY : No. We flash them to be sure there are no weak stems or similar 
defects. If one leaks it is likely to burn out in the 140- volt d-c test. I do not say 
the lamps are infallible and I am not particularly emphasizing this type of lamp. 
We. are primarily interested in answering the problem of lighting in a television 
studio. Any suitable type of lamp might be used. This is primarily a holder for 
an illumination device. We happened to use these lamps because they are effi- 
cient and are the lightest in weight that we could get. 

DR. GOLDSMITH: You could surround them with gauze, if necessary? 

MR. EDDY : They could be surrounded with gauze or wire. I have thought of 
doing so, but having no reason for it as yet I have not gone that far. 

MR. KURLANDER : The weakest part is just above the base, where the glass is 
subjected to great heat. Very severe strains are sometimes created in the glass, 
and the whole bulb may come off. 

MR. EDDY: In our early tests we expected something like that, and were very 
careful about putting the lamps close to a working set and lighting them with 
120 volts d-c in a very cold studio at about 65 F. We thought surely the lamps 
would break when putting on the voltage without dimmers. But in two or three 
months of experimentation we lost no bulbs and have had no accidents. 



MATHEMATICAL EXPRESSION OF DEVELOPER 
BEHAVIOR* 



J. R. ALBURGER** 

Summary. Characteristics of developing agents have been unified in a mathe- 
matical expression. The use of the analysis of developer behavior afforded by this 
expression has been helpful in providing a guide toward improving a developer with 
respect to any given characteristic. 

During experimentation with the "peptized sol" developer 1 it was 
observed that a curious effect was obtained when alkali concentra- 
tion was raised sufficiently high. The effect was first noticed in 
Duratol (para-benzyl-amino-phenol) . In a solution containing 0.2 
to 0.5 per cent sodium hydroxide, normal development was obtained. 
When the concentration was raised to 2 or 3 per cent a surface de- 
velopment evidenced itself. It seemed that the developer was simply 
not penetrating to the lower levels of the emulsion. This observation 
started off a series of investigations to see what effects of a similar 
nature could be obtained with other agents and what the factors of 
control were. In the course of the work, a number of interesting facts 
were discovered, many of which have given us new insight into the 
chemistry of developers. 

The importance of surface development may not seem immediately 
evident. There is, however, a reason for investigating this subject 
in detail. In the more or less classical Hurter and Driffield analysis 
of photographic physics, certain well defined laws are laid down. 
It seems that these laws change when certain conditions of concentra- 
tions in developer composition are used. According to the H&D 
analysis, presence of bromide in a developer shifts the intersection 
point of the extended straight-line portions of the characteristic 
curves down below the zero axis of density. 

The result of shifting this intersection point down is that the 
gamma becomes less affected by development time. With a de- 

* Presented at the 1940 Spring Meeting at Atlantic City, N. J.; received 
April 20, 1940. 

** RCA Manufacturing Co., Camden, N. J. 

282 



MATHEMATICAL EXPRESSION FOR DEVELOPER 



283 



veloper containing bromide, toe densities are inhibited, and in order 
to get low contrast suitable for negative development, it is necessary 
to underdevelop the film. When this is done, emulsion speed is lost. 
The effect of bromide on a developer is shown in Fig. 1. 

Under certain conditions, however, it is possible to move this 
point of intersection back up above the zero axis even though the 
potassium bromide concentration is above 10 grams per liter. This 
departure from the classical Hurter and Driffield theory led the writer 




FIG. 1. Effect of bromide upon a developer. 



to investigate the possibility that other extreme conditions might 
produce effects which would be useful. 

THE PEPTIZED SOL AND POLYMERIZATION 

An indication of a departure from the classical theory of developers 
evidenced itself when it became possible, through the use of the 
"polypeptized-sol" effect in buffering alkalinity to utilize extreme 
conditions in alkaline concentrations. By the addition of potassium 
alum to a solution of sodium hydroxide, a complex salt is formed 
which can be considered to be sodium aluminate. Strictly speaking, 



284 J. R. ALBURGER [j. s. M. P. E. 

the solution contains acid aluminate which is peptized on a few 
sodium aluminate molecules forming an agglomeration of molecules 
or a peptized group. All reactions in the solution exist in equilibrium, 
so that regardless of the concentration of alkali, there will be always 
a certain effect felt in the solution due to the potassium alum. The 
presence of the alum in a developer formula of this type serves two 
functions. First, it prevents swelling of the gelatin of the film even at 
temperatures as high as 110F. Second, it serves to harden the de- 
veloped image far beyond any point obtained even in an acid hardener 
fixing bath. For example, concentrations of sodium hydroxide as 
great as 200 grams per liter may be used in a developer at tempera- 
tures well above 100 as long as the solution is buffered with an 
amount of potassium alum equivalent to four-thirds the weight of the 
sodium hydroxide. This method of buffering the alkalinity of de- 
veloper solutions so as to minimize the physical effects of the alkali 
makes it possible to investigate the properties of agents when used 
in solutions containing such concentrations. 

As was stated before, the effect of surface development was first 
observed with the agent Duratol, which chemically is para-benzyl- 
aminophenol. It was observed in the case of this agent that solu- 
tions containing less than 10 grams per liter of sodium hydroxide 
developed normal contrast. When the concentration of sodium hy- 
droxide was raised to between 20 and 30 grams per liter, the de- 
veloped contrast was decreased. By examination of the film during 
development, it appeared that development was taking place mostly 
on the surface of the film. It was found that the greater the concen- 
tration of sodium hydroxide, the more pronounced this surface effect 
became. This particular surface effect will be referred to as "alka- 
linity surface effect. ' ' The appearance of this phenomenon aroused in- 
terest in the possibility that a similar effect might be obtained with 
other agents. Hydroquinone was tried and found to exhibit the sur- 
face effect starting at the concentration of about 60 grams per liter 
of sodium hydroxide. Glycine was tried and found to require about 
110 grams per liter of sodium hydroxide before the surface effect 
evidenced itself. 

An explanation for this surface effect was sought, a possibility being 
that the developer molecules were not penetrating into the depths of 
the emulsion. One conceivable mechanism would be that the "salt 
effect" of high concentrations of dissolved substances produces a 
physical effect on the gelatin to slow down the penetration of developer. 



Sept., 1940] MATHEMATICAL EXPRESSION FOR DEVELOPER 285 

However, another possibility appeared that the developer mole- 
cules themselves might become peptized into groups of molecules 
under the influence of large concentrations of sodium hydroxide. 
The large group thus formed would be unable to penetrate rapidly 
into the gelatin of the film. Having considerable energy due to the 
high concentration of sodium hydroxide, development near the sur- 
face would proceed rapidly so that full emulsion speed would be ob- 
tained while the developed gamma was reduced. 

It could be that the "salt effect" on the gelatin would evidence itself 
at less sodium hydroxide concentration on agents of high molecular 
weight. However, a number of facts observed in experiments indicate 
that the size of the developer molecule, while exerting a major in- 
fluence, is not the only factor involved. 

OH 
/\ OH 




FIG. 2. (Left) Duratol (benzyl-^-aminophenol) and (right) dibenzyl--amino- 

phenol. 



It appears that the surface effect is a function of the sodium hy 
droxide concentration. The effect also seems relatively dependent on 
the structure of the compound. Experiment bears this out some- 
what since para-benzyl-amino-phenol behaves normally in a weakly 
alkaline solution. When the sodium hydroxide concentration reaches 
about twenty grams per liter, surface development becomes apparent. 
In the case of glycin or hydroquinone, surface development is not ob- 
tained until a concentration of about 100 grams per liter is reached. 
The size of the developer molecule also should be expected to have a 
part in the surface effect. 

It was reasoned that if this were true, we should be able to obtain a 
similar effect of surface development by starting out with a developer 
composed of large molecules. Inasmuch as very few developers were 
available which had sufficient molecular weight, it was necessary to 



286 J. R. ALBURGER [j. s. M. P. E. 

synthesize agents. The first synthesis was an additional substitution 
in Duratol. Duratol consists of para-aminophenol with a benzyl 
group (C 6 H 5 .CH 2 ) substituted in place of one of the hydrogen atoms 
in the amino radical (Fig. 2). 

Para-dibenzyl-aminophenol is the same with the additional substi- 
tution of a benzyl group for the other hydrogen atom in the amino 
radical CH.C 6 H 4 N(CH 2 C 6 H 5 ) 2 . The compound thus formed has 
three benzene rings present in it as compared with two for the original 
Duratol. The molecular weight is slightly more than half again as 
great, and if the surface development were dependent on molecular 
size, we should expect a more pronounced effect from this agent. This 
was found to be true. The surface effect evidenced itself at a con- 
centration of about 5 grams per liter of sodium hydroxide. 

Several other syntheses were carried out, and the agents produced 
were investigated as to their properties in the matter of surface de- 
velopment. Substitution of groups containing benzene rings tended 
to reduce the solubility of the compound formed. Tetra-benzyl- 
para-amino aniline [N.C6H 4 .N(CH 2 .C6H 6 )4] is almost completely in- 
soluble even in very strong alkali (Fig. 3). 

CH 2 N 



>CH 2 N CH 2 
FIG. 3. Tetrabenzyl-/>-aminoaniline. 

However, what little of the material does go into the solution 
evidences an extremely pronounced surface effect. Full emulsion 
speed is obtained but the developed gamma is down below 0.2 or 0.1. 
The use of such a substance as a developer does not appear to be im- 
mediately worth while. However, a secondary effect arises which 
might conceivably be put to good use. After developing the original 
image in this developer, the film can be fully exposed to white light 
and redeveloped in ordinary developer, whereby the effect of re- 
versal is obtained. 

There are two other functions in developer behavior besides the 
alkalinity surface effect which are dependent on the alkalinity of the 
solution. First and most obvious is the alkalinity energy function. 
It is well known that amidol (2-4-diamino phenol) will develop in acid 



Sept., 1940] MATHEMATICAL EXPRESSION FOR DEVELOPER 287 

solution. Other agents require greater alkalinity before they become 
energized. In general, the energy of a developer in very strong acid 
solution approaches zero. At a certain pH, the energy rises rapidly in 
tan" 1 function and at high concentrations of alkali, approaches a maxi- 
mum value. It seems necessary to consider two factors in the energy 
function of the developing agent; both, however, would be dependent to 
a certain degree on the reduction potential of the developing agent. In 
the one case, there is the question of the pH at which the developer 
energy rises at its maximum rate. The other factor is what is the 
maximum value of energy or fogging energy of the developer. For 
most ordinary developing agents, the energy begins to rise at a point 
very closely above neutrality of solution. The maximum value of 
the energy involves, additionally, a certain function of the oxidation 
potential of the emulsion. 

The second effect, which heretofore has had only brief mention in 
any of the journals and publications, is what will be termed "acid 
surface effect." From time to time it has been mentioned that cer- 
tain fine-grained developers which operate in near-neutral solution 
exhibit an effect of surface development. In certain cases, developed 
images are found to be of very low contrast due to this effect. The 
term "acid surface effect" is used for want of a better expression of 
the phenomenon in question. It has been suggested that the alkaline 
surface effect is caused either by a "salt effect" on the gelatin or by 
the grouping together of developer molecules to produce large groups 
of molecules which diffuse but slowly into the emulsion being de- 
veloped. The acid surface effect may be considered to be caused by an 
effective exhaustion or decrease in energy of the developer during 
passage into the emulsion depths. Diminution of density due to 
partial development of the silver grains would be a contributing 
factor in the acid surface effect. Under conditions where the agent 
is not strongly energized by alkali, it may experience an effective 
exhaustion or slowing down of activity in the near neighborhood of a 
nucleus being developed. This would give much the same result, 
producing lowered contrast and a tendency toward fine grained 
images. 

Thus, as the pH is varied, a condition is found which gives maxi- 
mum image penetration and maximum contrast, and to either side 
of this pH value the image is confined more nearly to the emulsion 
surface and the contrast is diminished. If the low contrast is that 
corresponding to low pH, we have called it the "acid surface effect" 



288 



J. R. ALBURGER 



[J. S. M. P. E. 



(because low H is in the direction of acidity) even though the solu- 
tion may still be on the alkaline side of neutral. During the study of 
these phenomena, every available developing agent was investigated 
and it appears that for all these developers there is what might be 
called an "acid surface effect" whereby the maximum effect is ex- 
hibited in strongly acid solution. As the alkalinity is increased, the 
point at which the acid surface effect falls off in a tangential function 
and approaches zero, differs for various agents. To be sure, in a 
strongly acid solution the developer energy is very low, tending to 



p- AMI NO PHENVU CUC 




' TiTM BCMZYI. -^-AMINO ANILINE 

VL AMIUOPHEHOL 




11 U 



' i-V 



DRCXJl/INOWE 



VL-/- PflENVLCNE DJAMINE 

X pH 

FIG. 4. Characteristic curves for several developing agents. 




mask any acid surface effect which might be present in the developer. 
For example, hydroquinone is almost completely inactive in acid 
solution. There are cases, however, which exhibit this acid surface 
effect even in strongly alkaline solution. A good example of this is 
oxalyl-paraphenylenediamine. This material^exhibits an acid surface 
effect up to a concentration of about 10 grams per liter of sodium 
hydroxide. At these concentrations, the alkalinity energy is suffi- 
ciently great to allow convenient observation of the effect. When 
about 15 grams per liter of sodium hydroxide is used with this agent 
the acid surface effect diminishes rapidly, and normal development 
takes place at a concentration of between 25 and 30 grams of sodium 



Sept., 1940] MATHEMATICAL EXPRESSION FOR DEVELOPER 



289 



hydroxide per liter. Unfortunately, this compound is unstable and 
hydrolyzes in water solution. 

The point at which this acid surface effect falls off seems to be de- 
pendent partly on the reduction potential. Thus a substance which 
evidences pronounced acid surface effect can be expected to have a low 
reduction potential, although this is not always the case. There are 
other factors which have bearing on this function, such as the various 
possible substitutions into the composition of the developing agent. 



GAMMA DEPRESSION 



ENERGY 




P H 



PHENYLENEDIAMINE 



PEVELOPCR CURVE 

PROJECTION ON X ,Y PLANE 

PROJECTION ON X.Z PLANE 

FIG. 5. Three-dimensional representation of Fig. 4. 

Fig. 4 shows representative characteristic curves for several de- 
veloping agents. Note that the curve of gamma depression for p- 
phenylenediamine has a rise at both ends. A three-dimensional 
construction of the curve of developer behavior is illustrated in Fig. 
5. The curves shown in Fig. 4 are the projections of the developer 
curve on the x, y and x, z planes, respectively. Fig. 5 is another way 
of showing the relationship indicated in Fig. 4. 

It will be noted that the surface effect is not expressed by any 
definite numerical quantities. At best, only an arbitrary standard 
could be fixed upon, and the values of the constants in the equations 
would depend on the choice of this standard. The shape of the curves 



290 J. R. ALBURGER [j. s. M. P. E. 

turns out to be such that they can be expressed approximately by 
equations of the form shown below. 

Strictly speaking, we have two equations because the curved line 
which represents developer behavior lies in three dimensions; that 
is, we are plotting developer energy against alkalinity in one plane, 
and combining that with a relationship between alkalinity and sur- 
face effect. The surface effect in the final equation is an addition of the 
acid surface effect and the alkalinity surface effect. It appears from 
the behavior of the agents studied that the various functions take a 
tangential or, if one wishes, a tan" 1 form. It does not appear likely 
that there would be any appreciable error arising from this assumption. 

The shape of the tangential curves may be varied by choice of 
suitable constants; that is, the curves may be either widened, elon- 
gated, or shifted to the right or left. 

The following three equations express in most general terms the 
three functions : alkalinity surface effect, alkalinity energy, and acid 
surface effect, all as functions of H. 

X - a - b tan ^(y - \ = Alkalinity Surface Effect (I) 



X - d - e tan i(z - *I\ = Akalinity Energy (2) 

- X - g-h tanA/V - -) =0 Acid Surface Effect (5) 

from ,. tan 1 (, - | e ) - ^LlLf 



from 3, y = i tan" 

Curve which is summation along F ordinate 
Y = y + y' = c tan~ : 



Y = Surface effect (gamma depression) 

Z = Developer energy 

X = pH of the solution or NaOH concentration 



Sept., 1940] MATHEMATICAL EXPRESSION FOR DEVELOPER 291 

Increasing a shifts curve to right (X, Y Plane) 1 . . 

Increasing b elongates curve (X, Y Plane) > AH o * 

/ ir IT T-H \ AiK.-ouriace 

Increasing c widens curve (X , Y Plane) J 

Increasing d shifts curve to right (X, Z Plane) 1 

Increasing e elongates curve (X, Z Plane) > Alk. Energy 

Increasing / widens curve (X, Z Plane) J 



Increasing g shifts curve to left (X, Y Plane) j -. . 

Increasing h elongates curve (X, Y Plane) > 

/ ,, Tr N Acid Surf j 

Increasing i widens curve (X , Y Plane) J 



To make use of these equations, it was found expedient to enumer- 
ate a number of factors which have a bearing on the characteristics 
of a given developing agent. In this way a picture is afforded of 
developer behavior which allows more satisfactory choice of agents 
for a desired result. 

Dependents 

a Linkage factor depending on type of linkage groups 
b 

c Molecular size (no. of benzene rings) 
d Inverse reduction potential function 
e Reduction potential function 
/ Oxidation potential and reduction potential 
g Reduction potential function, also basic groups in molecule 
h Acidic groups present in molecule 

i Type of reaction products which inhibit development ; also reduction poten- 
tial variations which affect grain size 

The dependents enumerated here are merely a rough indication of 
the influences bearing on the behavior of a developing agent. By 
observation of the effect of substitution of certain groups in the de- 
veloper molecule, it has become possible to predict the characteristics 
of an agent in respect to surface effect and grain structure. 

For a picture negative developer, fine grain is desired. Observa- 
tion shows that if an agent is used in such a way that the operation is 
carried out on the acid surface characteristic, minmum grain size will 
be obtained. Full emulsion speed is desired and sufficient energy 
to overcome bromide effect. Thus we find it necessary to work 
on the high end of the alkalinity energy curve. The operating pH 
should also be considered due to the effect of pH on emulsion tur- 
bidity, swelling of the gelatin, and aerial oxidation. Accordingly it 
is possible to choose agents which have the necessary characteristics 



292 J. R. ALBURGER [j. s. M. p. E. 

for picture negative development or for variable-density sound 
negative development. 

In carrying through these investigations a radical departure from 
accepted photographic practice was found practicable and even 
necessary. First, it has been generally believed that the presence of 
bromide in a picture negative developer was very undesirable inas- 
much as emulsion speed would be diminished. However, by suitable 
choice of developing agents and operating conditions, it has been 
found possible to retain complete emulsion speed and shadow detail 
even with 10 grams per liter of bromide in solution. 

A second belief which has held sway is the idea that emulsion speed 
will be lost if grain size is diminished. Under certain circumstances 
this has been found to be decidedly not the case. Extremely fine grain 
similar to that obtained in a ^-phenylenediamine-sulfite developer 
has been obtained with emulsion speed and shadow detail equal to a 
high-energy M-Q developer. 

A third widely accepted idea is that fine-grain development is im- 
possible in strongly alkaline solution. Some of the experimental 
formulas tested contained as much as forty grams per liter of sodium 
hydroxide, which seems to be rather extreme alkalinity. However, 
fine grain was obtained with full emulsion speed and complete shadow 
detail. Unfortunately, with many thick negative emulsions, in- 
creased turbidity very often causes loss of detail even though the 
grain is fine. 

There are a number of considerations to be noted in the design of a 
picture negative or variable-density sound negative developer. 
Briefly, they are: 

(1) Fine grain 

(2} High resolving power 

(5) Correct H&D characteristic for the purpose to which the developer is to 
be put 

(4) Complete emulsion speed and shadow detail 

(5) Freedom from bromide inhibition 

(6) Minimum tendency toward oxidation by air 

The fact that developer characteristics may be unified in a mathe- 
matical expression has been extremely interesting, but the matter of 
prime importance is the fact that by use of the analysis of developer 
behavior afforded by these expressions, there has been provided a 
guide toward improving a developer with respect to any given char- 
acteristic. 



Sept., 1940] MATHEMATICAL EXPRESSION FOR DEVELOPER 293 

REFERENCE 

1 ALBURGER, J. R.: "RCA Aluminate Developers," J. Soc. Mot. Pict. Eng., 
XXXIII (Sept., 1939), p. 296. 

DISCUSSION 

MR. CRABTREE: Have you tried adding an inert substance, such as sodium 
sulfate, to the developer? It is well known that inert substances, such as sodium 
sulfate or magnesium sulfate, glucose, sugar, and so on, not only retard develop- 
ment but produce a decided surface effect. 

When potassium alum is neutralized with caustic soda, approximately the same 
weight of sodium sulfate is formed as the caustic soda used. I understand that 
quantities of caustic soda, of the order of 200 grams per liter, were used, which 
would produce 200 grams per liter of sodium sulfate, which in turn would produce 
a decided surface effect. 

MR. ALBURGER: That is true, and there is a certain relation between the two 
functions. However, the salting-out effect does not seem to be the entire story. 
As was mentioned about the ^-benzyl amino phenol, the surface effect became 
evident at 5 grams per liter of sodium hydroxide. 

MR. CRABTREE : What was the />H of the solution in the presence of 200 grams 
of sodium hydroxide? 

MR. ALBURGER: It could not be measured, because our meter goes only to 14, 
and we would have had to guess from there on. 

MR. EVANS: Do I understand that in this series of sodium hydroxide you 
maintained the alum ratio at four-thirds throughout the series? 

MR. ALBURGER: Yes. In all of this series we measured the concentration of 
sodium hydroxide, and each concentration was suitably balanced with four-thirds 
of the weight of potassium alum. 

MR. EVANS : The final equation you plot is a characteristic of such a series of 
aluminate concentrations? 

MR. ALBURGER: Yes. 

MR. EVANS: I take it that you are not proposing to extend your conclusions 
to the developing agent, as such, but just state it for such a series of solutions? 

MR. ALBURGER: At this time, yes. 

MR. CRABTREE : Did you encounter difficulty due to precipitation of alumina 
in the fixing bath? 

MR. ALBURGER: We encountered no trouble in that respect. It was thought 
for a while that we might have considerable trouble, but tests were made, and the 
only effect was more rapid deterioration. In other words, it would neutralize the 
acid in the fixing bath more quickly than an ordinary developer would. 



A MODERN STUDIO LABORATORY' 

G. M. BEST AND F. R. GAGE** 



Summary. A description of the new laboratory erected by Warner Bros, at 
Burbank, Calif., in 1938. No general release work is required of this laboratory, and 
the generous space provided is devoted exclusively to the developing and printing of 
the dailies, storage and handling of the negative, and the latest in air-conditioning 
and dust-removing equipment. Advantage has been taken of the recent develop- 
ments in rust-resisting and acid-proof metals, especially in the construction of the 
developing machine tanks. The description includes the method of operation through 
the dailies, negative cutting, printing, chemical mixing, silver recovery, and other 
essential processes. 



In the spring of 1938, Warner Bros, completed a new laboratory 
on a site adjacent to their Burbank lot, replacing their Hollywood 
laboratory which had served the studio for the previous fifteen years. 

The new laboratory differs from most of the West Coast laboratories 
in that it is designed for handling only the film involved in preparing 
pictures for release. All release work, except for three prints made 
for the Los Angeles area, is done by the Ace Film Laboratories in 
Brooklyn, N. Y. Therefore the primary functions of the new labo- 
ratory are not release problems, but are confined to developing the 
negative, printing the dailies therefrom, reprinting at a later date the 
tracks used for dubbing, cutting the negative, and finally the prepara- 
tion of the first answer, or preview composite print. In addition, 
all composite duplicate negatives and master prints for foreign re- 
lease are made on equipment especially designed for the purpose and 
not used for any other work. 

The main building of the new laboratory is shown in Fig. 1. It has 
been laid out with ample room for all departments, no function of the 
laboratory processes being impaired due to lack of space. Built 
entirely of reinforced concrete, the building was engineered to provide 
for future expansion, there being unoccupied space available on the 

* Presented at the 1940 Spring Meeting at Atlantic City, N. J. ; received 
April 20, 1940. 

** Warner Bros. Pictures, Inc., Burbank, Calif. 

294 



A MODERN STUDIO LABORATORY 



295 



second floor and an additional story can be built in the future with- 
out modifications to the existing building walls. All windows are of 
glass brick, being in the form of a continuous section, making available 
a maximum of illumination in those departments which can work in 
daylight. Modern air-conditioning has made possible the use of this 
type of window to especial advantage in a plant which must be kept 
free from dust. 

Although there are a number of emergency fire exits, only three 
doors are ordinarily used, and traffic is limited to two of the doors 




FIG. 1. Exterior of main building. 

during a normal day's work. This minimizes the difficulty due to 
tracking in of dust on the feet of employees, as both doors open into 
halls far from the printing and developing section. The greatest 
enemy of a motion picture laboratory is dust and every precaution for 
its elimination has been taken in the design of the building. 

The first floor plan is shown in Fig. 2, all departments except the 
projection rooms and the chemical mixing and storage being on this 
floor. The developing equipment occupies about forty per cent of the 
first floor space and consists of six machines designed and built by 
Warner Bros. The machines are built in pairs, each set of develop- 
ing and fixing tanks being located in a separate room, with exits into 



296 



G. M. BEST AND F. R. GAGE 



U. S. M. P. E. 



the hallways at each end. The main wash tanks and dryboxes are in a 
common room finished in white enamel and illuminated on two sides 
by glass-brick windows, this room being connected to the develop- 
ing rooms by a light-trap, the only one in the building. 

The first machine group is set aside for positive prints only, and is 
located directly opposite the door leading into the printing room, 
enabling the delivery of prints from the latter with a minimum of 



WARNER BROS. PICTURES, INC. 
FILM - PROCESSING LABORATORY 

FIRST FLOOR PLAN 




FIG. 2. First floor plan. 

delay. The second group consists of a machine for sound-track 
negative, with additional tanks which can be cut in if the machine is 
to be used for emergency positive developing. Another machine 
in the same room develops process keys and special work, with two 
sets of developing tanks as in the sound-track machine. 

The third machine group includes a machine for picture negative 
only, and the other is used for fine-grain duplicate negatives for 
foreign release. All doors leading into the developing machine rooms 
are permanently open, as the hallway is painted black and lighted 



Sept., 1940] 



A MODERN STUDIO LABORATORY 



297 



with green safelights, the first white light being in the hall around the 
corner, far enough away from the picture negative machine that it 
will not fog the fastest types of panchromatic film. The absence of 
light-traps in the hallway facilitates the plant operation to a remark- 
able degree. 

The printing room equipment for picture consists of eight Bell & 
Howell Model D printers, of which three have automatic light- 
changing panels and the remainder are hand-set. The sound printers 
which are shown in Fig. 3, consist of a group of four machines built 







FIG. 3. Sound-track printers. 






by A. J. Tondreau, head of the Camera and Laboratory Repair De- 
partment of the studio, during the past year, replacing a like number 
of modified Bell & Howell Model D printers. The new printers have 
been designed to print any type of sound-track required by the studio, 
although their principal work is ultraviolet variable-area. Arrange- 
ments for variable-density printing are included, together with 
filters and aperture changers for fine-grain duplicating master posi- 
tives or fine-grain duplicate negatives, all at a standard speed of 
seventy-two feet per minute. Previous printers used for fine-grain 
work required slow speeds in order to have sufficient exposure, but 



298 G. M. BEST AND F. R. GAGE tf. s. M. P. E. 

the development of a new type vacuum cooling chamber to house the 
printing light has made possible the use of Mazda lamps of sufficient 
intensity that these printers may operate at their standard speeds at 
all times for any type of work. 

In a small annex off the printing room are two Eastman Model 
lib sensitometers for turning out negative and positive strips for 
processing control; also a Duplex printer for registration prints 
and two Bell & Howell Model D picture printers equipped with 
vacuum-cooled high-intensity lamps for fine-grain picture printing. A 
modified Bell & Howell Model D printer is retained in this room for 
emergency printing of fine-grain sound master prints which will fog 
in the normal type positive safelight illumination, but by closing 
the door into the main printing room, fine-grain printing can be done 
without holding up the routine of the main printing room. 

The raw print stock is stored in a vault 900,000 square-feet in ca- 
pacity adjacent to the printing room, and in the outside hall is an- 
other vault of 650,000 square-feet called the "Overnight" vault, in 
which developed negatives are stored when the night shift goes home. 
Directly opposite the second group of developing machines is the 
the sound-track breakdown room, where all sound-track dailies are 
brought from the studio and the "NG" and "HOLD" takes broken 
out of the rolls, only the "Choice" takes being processed. 

Across from the third developing machine group is the picture 
negative breakdown room where all timing tests are broken out of the 
rolls before development. The "Test" system is used for picture 
timing, each "Choice" take having a short section of test exposure at 
the end. These tests are developed at normal time and inspected 
over opal glass inspection tables in the timing room. Changes in 
time of development are indicated by the timer and the work is proc- 
essed accordingly. 

At the turn of the hall, next to the drybox, is the positive assembly 
room. Here all prints are delivered from the take-up reels at the 
ends of the developing units and are mounted on reels if they are 
composite prints; or are synchronized, if separate sound-track and 
picture. Moviola equipment is used to synchronize scenes where 
there is difficulty in locating the start marks. In a room opposite the 
positive assembly are the polishing, waxing, and edge-numbering 
machines. Here the prints are waxed by the cold wax process and 
sent upstairs to the projection rooms, to be run at a standard speed 
of 90 feet per minute, There are no high-speed projectors, since no 



Sept., 1940] A MODERN STUDIO LABORATORY 299 

release printing is involved and normal studio routine does not re- 
quire it. 

The negative assembly room for pictures is equipped with stainless 
steel, linoleum-topped tables at which the negative is inspected and 
the choice takes removed and spliced into rolls for printing. In 
back of the negative room is the negative cleaning room, equipped 
with a revolving velvet-covered drum having a capacity of 1000 feet 
of negative. All negative after being cut and spliced is thoroughly 
cleaned and dusted. No traffic into the room other than the two 
men employed there is permitted, and the incoming air is filtered 
through special dust filters. 

Next to this group is the sound track-negative assembly room, 
where all sound-track is prepared for printing. Densitometer equip- 
ment for reading track densities, sensitometer strips, and negative 
fog density are installed, and all processing control for both picture 
and sound by sensitometry is determined at this point. 

In sequence down the hall are the shipping room, motor-generator 
room, humidity and temperature control boards, and the timing 
rooms. The negative timing room has twin inspection glass frames 
for the negative test strips, while the positive timing is done with a 
twin projector assembly which projects two Cinex strips simultane- 
ously, a frame at a time, permitting the comparison of the print to be 
timed with one of previously known characteristics. These pro- 
jectors have liquid and air-cooled light-sources, eliminating the 
danger of fire. 

In the wing of the building beyond the positive assembly room are 
the laboratory offices and the negative cutting room. In the latter 
the picture and sound-track negatives are matched to the cutting 
prints and the master negatives are prepared for release. The room 
has 21 linoleum-topped steel tables so that several pictures can be in 
work at one time. Before the cutting prints are allowed in the nega- 
tive cutting room, they are thoroughly dry-cleaned in an annex where 
a continuous type cleaning machine using a non-inflammable solvent 
is installed. Cutting prints are invariably covered with oil, grease 
pencil marks, and dirt, the cleaning process stripping off all foreign 
matter without manual aid. 

Next door is the chemical laboratory where the chemists run 
continuous tests on all solutions. Adjacent to the chemical labora- 
tory is a room where chemical fades are made. 

On the second floor are two large projection rooms having a throw 



300 G. M. BEST AND F. R. GAGE [J. s. M. P. E. 

of 56 feet each, with a 16-foot picture. Here all synchronized dailies 
and composite prints are run at standard speed. Projection of fine- 
grain unwaxed master prints for foreign release is handled in a third 
projection room located in the laboratory machine shop adjacent to 
the main building, where the projectors are equipped with felt shoes to 
prevent damage to the unwaxed film. 

The remainder of the upstairs floor space consists of unfinished 
rooms available for expansion. These rooms have been provided 
with adequate duct connections for all power, air-conditioning, 
vacuum, compressed air, and water which might be needed for any 
special processing that will be required in the future. 

In the basement, in the section underneath the printing and break- 
down rooms, is the chemical mixing and developer storage section. 
Three 1200-gallon and four 850-gallon tanks for developer storage 
are installed there, with a raised platform walk surrounding the tanks 
to facilitate inspection of the contents. Eight developer mixing 
tanks of 250 gallons each, of stainless steel, with motor-driven agita- 
tors, are located on the platform next to the storage tanks. Stainless 
steel piping connects the mixing tanks with the storage tanks, from 
which the developer is pumped to the machines through centrifugal 
pumps. All developing baths are filtered through filters made by 
the Commercial Filters Corp., using their cotton filter cells. 

In a specially isolated room, the walls of which are treated to 
prevent acid decomposition, are the hypo storage tanks and silver 
recovery plant. Next door is the boiler room in which two automatic 
75-hp gas or oil-fired boilers furnish heat for the air-conditionirig 
plant. In the space underneath the office wing of the building are 
the air-conditioning equipment, emergency power plant, vacuum 
and air supply units, and the power switchboard. Ample space for 
storage of empty film cans and reels and laboratory supplies, a neces- 
sary evil in all laboratories, is located at the extreme end of the wing. 

Outside the main building are the negative storage vaults (Fig. 4), 
in a building of reinforced concrete consisting of two stories, each 
floor having 12 vaults with a capacity of 1386 cans each, or a total 
possible footage capacity of about thirty-three million feet. Each 
vault is equipped with explosion vents and automatic sprinklers. 

The laboratory machine shop is combined with the camera repair 
section and occupies a large building which completes the laboratory 
group. This shop is equipped for any kind of light or heavy repairs 
to the laboratory and is operated under the direction of Mr. A. J. 



Sept., 1940] 



A MODERN STUDIO LABORATORY 



301 



Tondreau. Here all printing machines and other units are periodi- 
cally overhauled and serviced, this work being done without inter- 

ption to the laboratory routine. 

In this shop the developing machines were fabricated. They 
of the deep-tank, variable-elevator type, being improved designs 
of the same machines that have been in use for some years at the Ace 
Film Laboratories in Brooklyn and the old Warner Hollywood labo- 
ratory. The developer tanks are of stainless steel, 8 inches wide, 
60 inches long, and 10 feet deep, the individual tanks being divided 





FIG. 4. Negative storage vaults. 



in two sections called elevator sections. All rollers are of bakelite, 
there being eight sets to each elevator, with a total of nine loops of 
film. The lower set of rollers can be raised or lowered to shorten or 
lengthen the loops, thus permitting a fine adjustment of developing 
time without changing the speed of the film through the developer. 
At the end of each elevator there is a stainless steel driving sprocket, 
with a hard rubber friction roller for edge-guiding. The film remains 
totally immersed in the solution throughout development except 
when passing from one tank to another, reducing to a minimum the 
troubles from contact with the air during development. 



302 



G. M. BEST AND F. R. GAGE 



(J. S. M. P. E. 



Normal operating speed is 105 feet per minute, but the speed can 
be increased to 160 feet per minute through change in the driving- 
shaft speed made available .by a gear transmission located next to 




FIG. 5. Developing machine group. 



the driving motor. This can be seen in Fig. 5, showing two of the 
developing machines looking from the input end. The film-storage 
rack at the input has a capacity of 400 feet, allowing ample time for 
the operator to splice the individual rolls. 



Sept., 1940] A MODERN STUDIO LABORATORY 303 

The hypo tanks are of wood, the same size as the developer tanks, 
and at the end of the assembly is a rinse tank which removes a large 
portion of the hypo before the film passes through the wall into the 
washing and drying room. An air squeegee prevents water from 
dripping off the film during its air transit. The entire developer- 
hypo section of the machine is 46 feet long and is mounted on con- 
crete pedestals which are set in the basement floor. The bottoms 
of all tanks are 6 feet above the floor, permitting free access under- 
neath all tanks for inspection and plumbing repairs. The tops of the 
tanks stand three feet above the main floor, so that inspection and 
adjustment of the equipment is facilitated. 

Each tank compartment contains a light-weight elevator bar on 
which are mounted eight spools held in place by a channel frame of 
stainless steel which permits complete removal of the film and roller 
assembly for cleaning purposes. This operation is performed manu- 
ally since the entire unit weighs only 30 pounds. 

All developing, fixing, and washing tanks have force-feed circula- 
tion of the solutions at 15 Ibs. of pressure, the liquid being expelled 
from jets in the sides of eight vertically mounted, stainless steel pipes 
placed opposite each strand of film. It was found necessary to 
manufacture all stainless steel parts for the entire machine from the 
same type of steel, to avoid ruinous electrolysis. All fabricated steel 
was supplied by the A. J. Byer Co. of Los Angeles while the castings 
were made by the Electric Foundry Co. of Portland, Ore. 

The normal developing time for picture negative is 7 1 /* minutes 
at 66F., it being possible to vary the developing time from 5 J /2 to 
IP/2 minutes by loop-length changes without varying the speed of 
the film through the machine. Longer development is possible by 
slowing the speed of the drive shaft but has not been found necessary 
in practice. The picture negative developer is a modified form of 
Eastman D-76, maintained at a pTL of about 8.70. At normal 
development time, a gamma of 0.65 is averaged on Eastman Plus X 
film. 

For sound-track negative, a high-contrast metol-hydroquinone 
developer with a carbonate accelerator is used, the pH being kept 
at about 10.00; and for a gamma of 2.45 the film fog is kept at 0.05 
for a developing time of 5 minutes. No variable-density negative is 
processed at the present time, but occasional density prints are made. 

Positive development time of four minutes in a modified Eastman 
D-16 developer at 66F produces a gamma of 2,20 which is the aver- 



304 



G. M. BEST AND F. R. GAGE 



[J. S. M. P. E. 



age for all prints. The pR is maintained at about 10.15. Developer 
temperatures are kept constant to within 0.1 F by temperature 
controls made by the Brown Instrument Co., all solution tempera- 
tures being continuously recorded on Brown recorders, including 
humidity and temperature of drybox air. Processing conditions are 
checked by sensitometer strips, all types of development being under 
rigid sensitometric control. 

The hypo circulating system starts at the central storage tank in the 
basement and branches to all developing machines through stainless 




FIG. 6. Washing and drying equipment. 



steel pipes. A common return line delivers the hypo to the silver- 
recovery system, where the pure metallic silver is electroplated onto 
stainless steel stripping plates. The plating operation requires a 
supply of 105 amperes at 2 volts, the current supply being a Rectox 
rectifier. Continuous agitation of the hypo in the plating tank pre- 
vents conversion of the silver to silver sulfide, the current-density per 
square-foot of plating surface being about 1.0 ampere at 2 volts. All 
hypo mixing is done in the same room with the hypo storage tanks, 
thus isolating all work on the fixing baths from the developer solu- 
tions. 



Sept., 1940] A MODERN STUDIO LABORATORY 305 

Film washing is done in six tanks of two sections each, for each 
machine, these tanks being identical in design with the fixing tanks, 
including the pressure circulating system. Fig. 6 shows a general 
view of the wash room, with the roller frames partially elevated for 
cleaning. The normal time of washing is 18 minutes at 105 feet per 
minute. The water enters the two tanks closest to the drybox end, 
overflows to a pump, and is pumped to the next two tanks, where it 




FIG. 7. Drybox terminal. 

again overflows and is again pumped to the last two tanks, where it 
overflows to the sewer. By this arrangement, the amount of water 
used has been reduced by two-thirds as compared with the old plant. 
The exterior finish of the wash tanks is white enamel with stainless 
steel tops and trimming. 

The dryboxes are built in three sections, as shown in Fig. 7, the 
air being kept at a uniform temperature of 75 F dry-bulb. Each 
drybox unit contains a dehumidifier, fan assembly, and filter system. 
The air is constantly recirculated, the water being extracted and the 
air returned again to the drybox intake, assuring a dust-free air sup- 



306 G. M. BEST AND F. R. GAGE [j. s. M. P. E. 

ply at all times. Fig. 8 shows the air circulation fans and filter 
groups in the basement underneath the drybox units. 

The three sections of each developing machine are operated by 
separate power drives, and between each unit is a safety storage 
rack having a maximum capacity of 11 minutes running time, al- 
lowing any section of the machine to be stopped. These storage 
racks are normally set for 100 feet of storage. The total length of 




FIG. 8. Basement drybox construction. 

film in the negative machines is 5500 feet, so that about 52 minutes is 
required from the time the raw exposed stock is fed into the input, 
until it is wound up on the drybox terminal. The positive thread- 
ing length is about a thousand feet shorter due to less footage re- 
quired in the processing, with a total running time of 42 minutes. 
All controls are operated from the end of the dryboxes, with telephone 
and alarm signals connecting the inputs and outputs of the machines. 
Automatic trip signals indicate when the safety storage racks be- 
tween the units are approaching their empty or full condition, giving 
ample warning to the operators. 



Sept., 1940] A MODERN STUDIO LABORATORY 307 

On each side of the main wash-tank group is a set of tanks used for 
toning, reducing, or intensifying. With the present trend of sepia 
toning on many pictures, these tanks have proved very useful in 
handling such work. 

The system used for maintaining solution temperatures as well as 
for air-conditioning is a combination of artesian well water supply 
and artificial refrigeration. One well, adjacent to the building, 
sunk to a depth of 185 feet, supplies from 500 to 900 gallons per 
minute at 66 F through a 30-hp pump. This temperature does not 
vary more than 1 / i throughout the year, and is used for precooling 
in the summer and preheating in the winter, through coils located in 
the incoming air-stream. 

As an example of operation, assume an outside air temperature of 
100F, passing over a precooling coil carrying this 66 well water. 
The air delivered out of the coil system will be approximately 77, 
or a temperature drop of about 23, with a cost only of operating a 
small pump. The remaining temperature drop of the air is ac- 
complished in a second coil surface carrying chilled water, from the 
central storage system on which the Freon compressors are working, 
this drop amounting to about 10. From this it will be seen that 
the mechanical refrigeration plant is handling only about one-third 
of the total temperature drop, with the well water carrying the bal- 
ance. 

The central plant consists of four compressors, two evaporators, 
two condensers (cooled with well water), and a storage tank. This 
unit's sole function is making chilled water, which is in turn pumped 
through the building to the various coils and exchangers for condi- 
tioning of the building and the control of developer temperatures. 

The use of a number of small unit compressors rather than one or 
two large ones permits a new high in economical operation, in that 
the compressors come into operation in sequence, adding capacity in 
direct ratio to the load demand. These compressors operate in paral- 
lel in one common system, as do the condensers, and being entirely 
automatic, hand valves are eliminated regardless of the number of 
compressors in operation. As the chilled water demand is satisfied 
the compressors cut off in sequence, to a point where all are out of 
service. During an unprecedented heat wave in September, 1939, 
only two of the compressors operated continuously, with a third com- 
pressor cutting in for 10 minutes out of each hour. The fourth 
compressor was never required at any time. Servicing of compres- 



308 



G. M. BEST AND F. R. GAGE 



tf. S. M. P. E. 



sors, condensers, or other units of the system can be done without any 
danger of interruption to the plant. The use of small machines of 25 
tons each effects further saving in operation because of lower demand 
of power as shown by the demand meter. Should there be a power fail- 
ure for even a prolonged period, the machines are arranged to return to 
service in sequence, on the restoration of power, through a time-delay 
relay, preventing the full load of the machines from coming on the line 
simultaneously. 

The air-conditioning system maintains a temperature of 74 F 
dry-bulb with l / 2 accuracy, and a humidity control of l x /2 per cent at 




FIG. 9. Air-conditioning and emergency power plant. 



55 per cent relative humidity. All air-conditioning ducts are oversize 
and readily accessible. Fig. 9 shows a general view of the cooling 
plant, on the left being the compressors and condensers, in the center 
the cyclone air pumps, then the vacuum and air-compressor equip- 
ments, and to the right are the emergency power units, which are 
two Bardco plants consisting of a Ford V-8 motor driving a 5-kw 
generator, controlled by relays which operate on failure of the city 
power supply. These generators will take over the load of the 
developing and printing equipment within 5 seconds of power failure. 
Less than two weeks after the laboratory was put into operation, a 
power failure of some hours' duration throughout Burbank caused 
the emergency equipment to assume the load until all negative 



Sept., 1940] A MODERN STUDIO LABORATORY 309 

which was already in process could be run through the developing 
machines. 

Film coming into the laboratory is routed through the shipping 
and receiving room, where it is separated and sent to the respective 
breakdown rooms. In the case of the sound-track negative, the 
"Hold and "NG" takes are broken out of the rolls and only the 
"Choice" takes processed. The "NG" takes are held for 72 hours, 
and if no call is made for them by the production office they are 
spliced into 1000-ft rolls and used for printing sound-track dailies. 
A Bell & Ho well positive type splicer is installed in the breakdown 
room, and an early morning shift splices the "NG and "Hold" takes 
before the afternoon breakdown crew comes on duty. The "Hold" 
takes are retained in the outside vault until the picture is released, at 
which time they are also spliced and used for printing. Even though 
the latter group of rolls be held for a year, the stock is still suitable 
for printing purposes, as it is from 8 to 10 printer points faster than 
standard positive when new, and at the end of a year is still several 
points faster than the latter. No new print stock is used for dailies, 
there being a surplus of "Out" takes after all sound dailies are printed, 
this excess being used for printing a dupe negative off the cutting 
sound and picture prints, from which work prints are made for the 
music and re-recording departments in the studio, for use during 
scoring and dubbing operations. 

Picture negative is delivered to the picture breakdown room, where 
all timing tests are broken out of the rolls before development. Al- 
though the "Test" system is employed for picture timing, the nega- 
tive bath is set by a combination of sensitometric, photographic, 
and chemical tests to produce a gamma of 0.65 at 7 l /% minutes de- 
velopment time. Each "Choice" take has a short section of test ex- 
posure which is developed at normal time and inspected in the nega- 
tive timing room. Changes in time of development as indicated by the 
timing operator are made, and the work is processed accordingly. 
All takes whether "Choice," "NG," or "Hold" are developed. 

Both types of negative are delivered from the drybox terminals 
to their respective negative assembly rooms. The "Choice" takes of 
pictures are broken out of the negative and assembled into 1000 ft 
rolls for printing. The sound-track negative, which is all of the 
ultraviolet push-pull type, is measured for density, and the scenes 
are then spliced into rolls for printing. This work is usually handled 
between 4 p. M. and midnight, by which time all production work 



310 G. M. BEST AND F. R. GAGE [J. s. M. P. E. 

has usually ceased. The printing and positive developing machine 
crews report at 5 A. M. and all dailies are timed and printed by 9 A. M., 
at which time the synchronizing crews report. As soon as the reels 
are synchronized they are run in the projection rooms and delivered to 
the studio. 

Optical printing, trick photography, and titles are made by the 
process department on the main studio lot and the negative is sent 
to the laboratory for processing. All separate sound-track prints for 
re-recording purposes are made on Eastman type 1361 fine-grain stock, 
printed by the day shift after the dailies are finished, as it is necessary 
to increase the time of development of the fine-grain stock by cutting 
in additional tanks in the developing section. The fine-grain com- 
posite master print used for printing the foreign duplicate negatives is 
exposed on Eastman type 1365 stock, and is developed in the pic- 
ture negative developer to a gamma of 1.25. The duplicate nega- 
tives are developed in the special machine set aside for that purpose, 
and additional sets of air-squeegee jets are installed between the 
wash tanks and the dryboxes to remove all water spots, to which this 
film is especially sensitive. 

From the above discussion it can be seen that the laboratory is 
able to turn out high-quality work with no part of the process im- 
paired because of the requirements for speed. 

DISCUSSION 

MR. CRABTREE: We in the research field often hesitate to recommend new 
formulas, because we think that possibly the laboratories already have too many. 
Just what is the feeling of a laboratory superintendent toward new formulas? 
Does he have spare tanks, so that he can try them out, and how big a job is it to 
change over to something different from what he is using? 

MR. SPRAY: It is not the formula as originally written on paper that counts, 
but the maintenance of that formula in a certain definite concentration at all times. 
In other words, it is a standardization problem, rather than so many grams of this 
and so many grams of that. It is a matter, in other words, of chemical control. 
Perhaps for negatives where we want a little more contrast, or for sound-track 
negatives, particularly in variable-area where we like to build up a good black, get- 
ting our density rather through development than through exposure, we use a de- 
veloper which is a little more energetic and we go to a little higher gamma. But 
outside of that we are not particularly interested in the formulas, as such ; we are 
rather interested in what they attempt to do. 

MR. CRABTREE: Do you have any spare systems or spare tanks? How many 
different solutions with accompanying replenishing systems do you have in the 
laboratory? 



Sept., 1940] A MODERN STUDIO LABORATORY 311 

MR. SPRAY: We have enough different solutions to satisfy the requirements 
of the different emulsions. Each is in a separate system. We do not try to put 
different emulsions through one bath. 

MR. CRABTREE : I think that Mr. Gage said that he had eight at the time of 
the last convention in Hollywood. I wondered whether the number had in- 
creased. 

MR. HYNDMAN: Each laboratory has the number of formulas and pieces of 
equipment for those formulas that are necessary within economic demand. In 
other words, some laboratories develop negative sound-track, negative pictures, 
and negative dupes, all in the same bath; whereas other laboratories develop 
each of these materials in a separate solution. To my knowledge there is no 
laboratory in Hollywood or in New York that has a developing machine in which 
experimental testing can be done. If any formula were to be tested experimentally 
to ascertain whether it were suitable, it would be necessary to cut production on 
at least one unit for that time. Unfortunately, for individualized testing it is 
quite common practice to have all the developing machine units tied into the same 
circulating system. Consequently, the cost of making an experimental test of a 
formula is often very high, because, depending upon the laboratory 1000 to 9000 
gallons of the developer have to be mixed. 

MR. CRABTREE : MGM, for instance, has a number of small units for negative 
development, each complete in itself. It would not seem to be a very difficult 
matter to try out an experimental developer under that system. 

MR. HYNDMAN : I believe that MGM is the only laboratory in the United States 
that has that system; all other laboratories have the centralized circulation 
system. 

I did not quite gather whether you meant that possibly the laboratories were 
against testing a new formula or were not willing to change from their present 
standard. I believe any laboratory is willing to try any formula that is recom- 
mended provided it can be adapted partially to their conditions before the formula 
is put into the machine. In other words, it may be necessary to cut down or raise 
the concentrations of certain chemical constituents to meet their processing con- 
ditions. 

MR. BEST:* Answering Mr. Crab tree's question regarding spare tanks and 
facilities for trying out experimental developers, two of the developing machines 
are equipped with spare tanks in the developer section. We have frequently used 
these tanks for experimental developers as well as to speed up the change-over from 
one type of developer to another in the same machine. 

Unlike a continuously operated release print laboratory, all developers are 
dumped into the sewer from time to time and entirely new solutions mixed. There 
are normally six solutions stored in the basement, these being the picture positive, 
process key positive, picture negative, process picture negative, dupe picture 
negative, and sound-track negative. Any of these developers can be pumped to 
any machine in the plant, but are normally pumped to the machine reserved for 
the work for which the developer is designed. 

There is usually an empty storage tank available in the basement, and it is 

* Communicated. 



312 G. M. BEST AND F. R. GAGE [j. s. M. P. E. 

easy to mix up the minimum of 400 gallons of solution required to operate the 
tanks and circulating system and try out any new developer recommended by the 
film manufacturers. That was one of the reasons for installing the spare de- 
veloping tanks, so that the regular work could go on undisturbed, and during a 
breathing spell the auxiliary tanks with the special developer could be threaded 
to the input rack and hypo tanks, bridging out the regular developer, all at 5 
minutes' notice. During recent months, new sound-track negative formulas 
have been tried out under these conditions, and where these experiments have 
proved the new formula had advantages over the one in use, changes were gradu- 
ally made in the regular formula to incorporate these improvements. 

No new formula recommended by the makers of the film we are using is ever 
passed by without adequate experimental tests and we feel that the studio 
laboratories in particular are very open-minded on the subject of advancements 
in this phase of the art. 

DR. H. P. GAGE: How were the n. g. takes later used for printing? 

MR. SPRAY: The sound-track prints having just a small portion of their film 
used for that purpose, can be used again to print a picture or a track on the op- 
posite side. 

MR. KELLOGG: Mr. Hyndman spoke of the adaptation of a developer to par- 
ticular laboratory conditions. It is difficult for me to see that developer formulas 
need to be materially changed for different laboratories, unless for the purpose 
of conforming to what the operators are accustomed to. As far as sound-tracks 
go, all who are making variable-area tracks are shooting for about the same final 
result and the same is true of those who are working with variable-density re- 
cordings. Practically the same thing could be said about picture quality. There 
may be a difference in the speeds of operation of the developing machines, or in 
their agitation or filtering systems. Apart from these factors, why should there 
be differences? 

MR. SPRAY: There should not necessarily be any differences; but the end is 
what we are trying to arrive at. RCA wants a definite density at a definite gamma, 
and we give it to them. You must remember that when sound came out first, 
there were not any published formulas for that purpose. 

The making up of a formula in a small amount is one thing, but the maintaining 
of it continuously is an entirely different problem. We at the Ace Laboratory 
have had a bath running over a couple of years that has not been remade at all, 
but has been kept continuously operating. That is an entirely different problem 
from the publishing of a formula made up for the moment. Such a lot of things 
take place over a long period of time under operating conditions. 

MR. KELLOGG : I suppose it is a difficult thing to get a complete answer to my 
question. I wondered how much of it was purely psychological, or a matter of 
what people are familiar with, and how much of the difference is really necessitated 
by inherent differences in the developing machines and their set-up. 

MR. SPRAY: One important factor that does not come out in formulas is the 
speed of the film through the bath. 

MR. IVES: The formula as you write it on paper is that of absolutely fresh and 
unused developer. In the machine system, its state is quite different. It is at all 
times in a partially exhausted condition, because it does not just hit the film and 
run off into the sewer. Consequently, the formula as used in the product of the 



Sept., 1940] A MODERN STUDIO LABORATORY 313 

original formula, plus the treatment which has occurred is the course of running 
a certain amount of film through it in a certain machine, with exposure to various 
local conditions. Since the machine designs vary widely, the results obtained with 
a given starting formula vary rather widely from one laboratory to another. 

In order to have the activity of the bath consistent with the running speed of 
the machine, some adjustment of the activity is frequently necessary. Of course, 
economics also enter into these things. 

MR. KELLOGG: Would it be right to say that the principal differences in re- 
quirements of different laboratories to achieve essentially the same result (for 
example, to process a variable-area sound recording up to a certain desirable 
density) would be the feet per minute that the film travels, and the equipment for 
producing agitation or circulation? Those are the only things that seem to me 
necessarly different in different laboratories. If it were not for such things as I 
have just mentioned, which are due to differences in equipment, you might well 
standardize on a formula and method of replenishment. Is that right? 

MR. EVANS: When four laboratories say they are using the same formula, they 
are not, in the ordinary case. They start out with the same formula, but the 
technic of replenishment leads to a different formula in all four laboratories. 
Agitation and temperature and speed of the machine all enter into the picture, 
very decidedly; but in addition, there is the difference that four persons, each 
using his own technic of replenishment, will arrive at four different stable con- 
ditions. 

I would like to enter a plea, now that we have analytical methods for develop- 
ers, that we start writing the formula for the used developer, and not the one that 
we start with. 

MR. SPRAY : One more factor enters : Emulsions are kept remarkably uniform. 
The variations in them are very small, especially considering the fact that a photo- 
graphic emulsion is one of the most complicated chemical products made on a large 
scale. They do vary somewhat, however, enough to cause us to change our speed 
of development and time of exposure. 

DR. NICHOLSON: At the Signal Corps Photo Laboratory we are constantly 
supplying prints of negatives that may have been exposed and developed any 
time during the last twenty-five years. These negatives include the World War 
negatives, which were developed somewhere near the front lines without any 
sensitometric control. The development gamma of these negatives probably 
varies from 0.50 to 0.90. 

The superintendent of the laboratory inspects the negative and chooses a 
positive gamma that will produce an approximate overall gamma of 1.30. His 
choice may be any positive gamma from 1.50 to 2.50. 

Regardless of the development gamma our positive developing machine must 
be operated at top speed in order to meet our release schedule. The maximum 
developing time with the elevators all the way down is 4 l /s minutes. The mini- 
mum development time with the elevators all the way up is 2 3 / 4 minutes. The 
first requirement of our positive developer, therefore, is that a gamma of at least 
2.50 is obtained in 4*/3 minutes and a gamma of not more than 1.50 is obtained 
in 2 3 /4 minutes. 

All prints are exposed at the same speed with the same printing lamp. The 



314 G. M. BEST AND F. R. GAGE 

voltage on the printing lamp can be varied from 90 to 125 volts. Below 90 volts 
the lamp becomes unstable and above 125 volts the life of the lamp is decreased. 

The second requirement of our positive developer, therefore, is that at a de- 
velopment gamma of 2.50 the developer should not give too much density to per- 
mit printing light negatives with 90 volts on the printing lamp, and that at a 
development gamma of 1.50 the developer should give sufficient density to permit 
printing heavy negatives with 125 volts on the printing lamp. 

Experience has taught us that these two requirements of gamma and density 
are approximately fulfilled if a development of 3 3 /4 minutes gives a gamma of 2.20 
and the density of step 6 on an Eastman 115 sensitometric strip is 0.60. No 
standard developer will give these results. In order to get these results a developer 
that gave a gamma less than 2.20 and a density less than 0.60 in 3 3 /4 minutes had 
to be mixed and put into the developing machine. By slight increases in the de- 
veloper constituents and many tests, the desired results were finally obtained. 

This process is called adapting a positive developer to suit the requirements of 
a particular laboratory. Developers will always have to be adapted to meet par- 
ticular requirements unless developing machines and laboratory methods become 
standardized. 

MR. CRABTPEE: What method of lubrication of the film is employed? 

MR. SPRAY: At Hollywood they use the edge-waxing system, which has been 
found satisfactory. 



CURRENT LITERATURE OF INTEREST TO THE MOTION PICTURE 

ENGINEER 



The editors present for convenient reference a list of articles dealing with subjects 
cognate to motion picture engineering published in a number of selected journals. 
Photostatic copies may be obtained from the Library of Congress, Washington, D. C., 
or from the New York Public Library, New York, N. Y. Micro copies of articles 
in magazines that are available may be obtained from the Bibliofilm Service, Depart- 
ment of Agriculture, Washington, D. C. 



Acoustical Society of America, Journal 

12 (July 1940), No. 1 

Acoustic Impedance of Commercial Materials and the 
Performance of Rectangular Rooms with One Treated 
Surface (pp. 14-23) 

Sound Control Apparatus for the Theater (pp. 122-126) 
Sound Measurement Objectives and Sound Level Meter 
Performance (pp. 150-156) 



American Cinematographer 

21 (August 1940), No. 8 

The Light-Meter and Its Relatives (pp. 342-344) 
Cinematographers Show How to Achieve Production 
Economies (pp. 360-362) 

British Journal of Photography 

87 (June 28, 1940), No. 4182 

Progress in Colour (pp. 313-314) 

87 (July 5, 1940), No. 4183 

Progress hi Colour (pp. 323-324) 

87 (July 19, 1940), No. 4185 

Progress in Colour (pp. 351-352) 

Communications 

20 (July 1940), No. 7 

Fundamentals of Television Engineering, Pt. 10 (pp. 
7-8, 18-19) 

Electronics 

13 (July 1940), No. 7 

Embossing at Constant Groove Speed a New Record- 
ing Technique (pp. 26-27, 62-64) 
A Picture Signal Generator, IV (pp. 28-31) 



L. L. BERANEK 
H. BURRIS-MEYER 

J, M. BARSTO 



D. B. CLARK 



F. EVEREST 



E. E. GRIFFIN 
J. A. BRUSTMAN AND 
M. P. WILDER 

315 



316 



CURRENT LITERATURE 



International Projectionist 

15 (June 1940), No. 6 

Sound Reinforcing System Data (pp. 7-8, 11-12, 29-30) P. P. MELROY 
Efficient Projection Supervision (pp. 22-22) H. RUBIN 



Motion Picture Herald (Better Theatres Section) 

140 (July 29, 1940), No. 4 
The Search for Better Projection Light (p. 10) 
Reviewing the New D-C Arc Lamps (pp. 35-36, 38-40) 



F. H. RICHARDSON 



Optical Society of America, Journal 

30 (July 1940), No. 7 
Production Color Analysis of Kinescope Screens (pp. 

295-296) T. B. PERKINS 

Optimum Efficiency Conditions for White Luminescent 

Screen in Kinescopes (pp. 309-315) H. W. LEVERENZ 



1940 FALL CONVENTION 
SOCIETY OF MOTION PICTURE ENGINEERS 



HOLLYWOOD ROOSEVELT HOTEL 

HOLLYWOOD, CALIFORNIA 
OCTOBER 21st-25th, INCLUSIVE 



Officers and Committees in Charge 

E. A. WILLIFORD, President 

N. LEVINSON, Executive Vice-P resident 

W. C. KUNZMANN, Convention Vice-President 

J. I. CRABTREE, Editorial Vice-President 

L. L. RYDER, Chairman, Pacific Coast Section 

H. G. TASKER, Chairman, Local Arrangements Committee 

Pacific Coast Papers Committee 

C. R. SAWYER, Chairman 

L. A. AICHOLTZ C. FAULKNER W. A. MUELLER 

O. O. CECCARINI C. N. BATSEL J. STEWART * 

F. M. FALGE H. G. TASKER 

Reception and Local Arrangements 

H. G. TASKER, Chairman 

N. LEVINSON G. F. RACKETT E. HUSE 

K. F. MORGAN H. W. MOYSE J. O. AALBERG 

P. MOLE W. C. MILLER R. H. McCuLLOUGH 

A. M. GUNDELFINGER W. A. MUELLER J. M. NlCKOLAUS 

H. W. REMERSCHIED C. L. LOOTENS E. H. HANSEN 

G. S. MITCHELL W. V. WOLFE R. G. LINDERMAN 
L. D. GRIGNON E. C. RICHARDSON F. M. FALGE 



Registration and Information 

W. C. KUNZMANN, Chairman 
C. W. HANDLEY J. FRANK, JR. 

S. HARRIS W. R. GREENE 

317 



318 



H. T. KALMUS 
E. HUSE 
L. L. RYDER 
C. DUNNING 

R. G. LlNDERMAN 



FALL CONVENTION 
Banquet and Dance 

N. LEVINSON, Chairman 
G. S. MITCHELL 
P. MOLE 
H. G. TASKER 
W. C. MILLER 

R. H. McCULLOUGH 



[J. S. M. P. E. 



G. F. RACKETT 
J. O. AALBERG 
K. F. MORGAN 
H. W. MOYSE 
J. L. COURCIER 



Hotel and Transportation 



W. C. HARCUS 
F. L. EICH 
E. M. HONAN 
H. R. LUBCKE 
W. E. THEISEN 



G. A. CHAMBERS, Chairman 

L. M. HOFFMAN 

S. P. SOLOW 

D. P. LOYE 

D. J. BLOOMBERG 

F. J. DURST 



K. B. LAMBERT 

F. O'GRADY 

A. C. BLANEY 
D. B. BROWN 
J. G. FRAYNE 



J. O. AALBERG 
C. W. HANDLEY 
W. F. RUDOLPH 
J. M. NICKOLAUS 
J. K. MILLIARD 



Convention Projection 

H. GRIFFIN, Chairman 
H. A. STARKE 
L. E. CLARK 
M. S. LESHING 
A. F. EDOUART 
I. SERRURIER 



J. DURST 

R. H. McCULLOUGH 

H. W. REMERSCHIED 
H. I. REISKIND 
W. W. LINDSAY, JR. 



Officers and Members of Los Angeles Projectionists Local No. 150 



Ladies' Reception Committee 



MRS. H. G. TASKER 
MRS. E. C. RICHARDSON 
MRS. G. F. RACKETT 
MRS. H. W. MOYSE 
MRS. L. E. CLARK 
MRS. G. S. MITCHELL 



MRS. L. L. RYDER, Hostess 
assisted by 

MRS. N. LEVINSON 
MRS. P. MOLE 
MRS. C. W. HANDLEY 
MRS. K. F. MORGAN 
MRS. W. C. MILLER 
MRS. B. KREUZER 

MRS. A. M. GUNDELFINGER 



MRS. E. HUSE 
MRS. G. A. CHAMBERS 
MRS. J. O. AALBERG 
MRS. R. H. MCCULLOUGH 
MRS. C. DUNNING 
MRS. F. J. DURST 



Miss Ruth Williams, Social Director, Hollywood Roosevelt Hotel 



L. A. AICHOLTZ 
W. A. MUELLER 



Publicity 

J. HABER, Chairman 
W. R. GREENE 
G. CHAMBERS 



S. HARRIS 

A. M. GUNDELFINGER 



Sept., 1940] FALL CONVENTION 319 

New Equipment Exhibit 

B. KREUZER, Chairman 

P. MOLE F. J. DURST J. G. FRAYNE 

C. N. BATSEL O. F. NEU H. W. REMERSCHIED 

K. F. MORGAN F. M. FALGE C. R. DAILY 

P. F. HARPER G. H. WORRALL C. W. HANDLEY 

Headquarters 

Headquarters of the Convention will be the Hollywood Roosevelt Hotel, where 
excellent accommodations are assured. A reception suite will be provided for the 
Ladies' Committee, and an excellent program of entertainment will be arranged 
for the ladies who attend the Convention. 

Daily hotel rates to SMPE delegates will be as follows (European Plan) : 

One person, room and bath $ 3 . 50 

Two persons, double bed and bath 5.00 

Two persons, twin beds and bath 6 . 00 

Parlor suite and bath, 1 person 8.00-14.00 

Parlor suite and bath, 2 persons 12 . 00-16 . 00 

Room reservation cards will be mailed to the membership early in September, 
and should be returned to the Hotel immediately to be assured of satisfactory 
accommodations. 

Indoor and outdoor garage facilities adjacent to the Hotel will be available to 
those who motor to the Convention. 

Members and guests of the Society will be expected to register immediately upon 
arriving at the Hotel. Convention badges and identification cards will be sup- 
plied which will be required for admittance to the various sessions, studios, and 
several Hollywood motion picture theaters. 

Railroad Fares 

The following table lists the railroad fares and Pullman charges: 

Railroad Fare Pullman 

City (round trip) (one way) 

Washington $132 . 20 $22 . 35 

Chicago 90.30 16.55 

Boston 135.00 23.65 

Detroit 106.75 19.20 

New York 135.00 22.85 

Rochester 124 . 05 20 . 50 

Cleveland 111.00 19.20 

Philadelphia 135.00 22.35 

Pittsburgh 117.40 19.70 

The railroad fares given above are for round trips. Arrangements may be 
made with the railroads to take different routes going and coming, if so desired, 



320 FALL CONVENTION [j. s. M. P. E. 

but once the choice is made it must be adhered to, as changes in the itinerary may 
be effected only with considerable difficulty and formality. Delegates should 
consult their local passenger agents as to schedules, rates, and stop-over privileges. 

Technical Sessions 

The Hollywood meeting always offers our membership an opportunity to be- 
come better acquainted with the studio technicians and production problems. 
Technical sessions will be held in the Blossom Room of the Hotel. Several eve- 
ning meetings will be arranged to permit attendance and participation by those 
whose work will not permit them to be free at other times. The Local Papers 
Committee is collaborating closely with the General Papers Committee in arrang- 
ing the details of the program. 

Studio Visits 

The Local Arrangements Committee is planning visits to several studios during 
the Convention week. Details will be announced in the next issue of the JOURNAL. 
Admittance to the studios will be by registration card or Convention badge only. 

New Equipment Exhibit ' 

An exhibit of newly developed motion picture equipment will be held in the 
Bombay and Singapore Rooms of the Hotel, on the mezzanine. Those who wish 
to enter their equipment in this exhibit should communicate as early as possible 
with the General Office of the Society at the Hotel Pennsylvania, New York, N. Y 

Semi- Annual Banquet and Dance 

The Semi-Annual Banquet of the Society will be held at the Hotel on Wednes- 
day, October 23rd, in the Blossom Room. A feature of the evening will be the 
annual presentations of the SMPE Progress Medal and the SMPE Journal Award. 
Officers-elect for 1941 will be announced and introduced, and brief addresses will 
be delivered by prominent members of the motion picture industry. The eve- 
.ning will conclude with entertainment and dancing. 

The Informal Get-Together Luncheon will be held in the Florentine Room of 
the Hotel on Monday, October 21st, at 12:30 p. M. 

Motion Pictures 

At the time of registering, passes will be issued to the delegates to the Conven- 
tion, admitting them to the following motion picture theaters in Hollywood, by 
courtesy of the companies named: Grauman's Chinese and Egyptian Theaters 
(Fox West Coast Theaters Corp.), Warner's Hollywood Theater (Warner Brothers 
Theaters, Inc.), Pantages Hollywood Theater (Rodney Pantages, Inc.). These 
passes will be valid for the duration of the Convention. 

Ladies' Program 

An especially attractive program for the ladies attending the Convention is 
being arranged by Mrs. L. L. Ryder, hostess, and the Ladies' Committee. A suite 



Sept., 1940] FALL CONVENTION 321 

will be provided in the Hotel, where the ladies will register and meet for the 
various events upon their program. Further details will be published in a suc- 
ceeding issue of the JOURNAL. 

Points of Interest 

En route: Boulder Dam, Las Vegas, Nevada; and the various National Parks. 

Hollywood and vicinity: Beautiful Catalina Island; Zeiss Planetarium; Mt. 
Wilson Observatory; Lookout Point, on Lookout Mountain; Huntington Library 
and Art Gallery (by appointment only) ; Palm Springs, Calif. ; Beaches at Ocean 
Park and Venice, Calif.; famous old Spanish missions; Los Angeles Museum 
(housing the SMPE motion picture exhibit); Mexican village and street, Los 
Angeles. 

In addition, numerous interesting side trips may be made to various points 
throughout the West, both by railroad and bus. Among the bus trips available 
are those to Santa Barbara, Death Valley, Agua Caliente, Laguna, Pasadena, and 
Palm Springs, and special tours may be made throughout the Hollywood area, 
visiting the motion picture and radio studios. 

Those who wish to visit San Francisco may arrange for stop-over privileges 
when purchasing their railroad tickets. Arrangements have been made with the 
Hotel Mark Hopkins for single accommodations for $5 daily and double with twin 
beds for $7, both with baths. The Fairmont Hotel also extends a rate of $4 single 
and $6 double, with bath. Reservations may be made by writing directly to the 
Hotel. 

W. C. KUNZMANN, 

Convention Vice-f 'resident 



SOCIETY ANNOUNCEMENTS 



NOMINATIONS OF SOCIETY OFFICERS FOR 1941 

At a meeting of the Board of Governors held at New York on July 19th, the 
following nominations of officers for 1941 made by the nominating committee 
were confirmed: 

President **E. A. HUSE 

Executive Vice-P resident *H. GRIFFIN 

Editorial Vice-President *A. C. DOWNES 

Convention Vice-P resident *W. C. KUNZMANN 

Secretary *P. J. LARSEN 

Treasurer *G. FRIEDL, JR. 

Governors (Two to be elected) *M. C. BATSEL 

*F. E. CARLSON 
*E. K. CARVER 
**L. L. RYDER 
* Resides in East ** Resides in West 

All the officers and governors are elected for two years with the exception of 
the Secretary and Treasurer, whose terms are one year each. Two of the above- 
mentioned nominees for Governor are to be elected. 

Officers whose terms expire December 31, 1940, are as follows: 

E. A. WILLIFORD, President 

S. K. WOLF, Past-President 

N. LEVINSON, Executive Vice-President 

J. I. CRABTREE, Editorial Vice-President 

W. C. KUNZMANN, Convention Vice-President 

J. FRANK, JR., Secretary 

R. O. STROCK, Treasurer 

M. C. BATSEL, Governor 

H. G. TASKER, Governor 

Ballots for voting on these nominees are being mailed to the voting membership 
of the Society, and announcement of the results will be made at the 47th Semi- 
Annual Banquet on October 23rd, during the approaching Fall Convention at 
Hollywood. 

ATLANTIC COAST SECTION 

At a recent meeting of the Board of Managers of the Atlantic Coast Section, 
the following nominations of officers for 1941 were made: 

Chairman R. O. STROCK 

Secretary-Treasurer J. A. MAURER 

322 



SOCIETY ANNOUNCEMENTS 323 

Managers (Three to be elected P. C. GOLDMARK 
for two-year terms) H. E. WHITE 

W. H. OFFENHAUSER, JR. 
R. B. AUSTRIAN 

Managers (Three to be elected H. B. CUTHBERTSON 
for one-year terms) F. C. CAHILL, JR. 
J. A. NORLING 
M. E. GILLETTE 

Officers and managers of the Section whose terms expire December 31, 1940, 
are as follows: 

P. J. LARSEN, Chairman 
D. E. HYNDMAN, Past-Chairman 
J. A. MAURER, Secretary-Treasurer 
H. GRIFFIN, Manager 

In a proposed amendment of the By-Laws, described in following paragraphs, 
the Boards of Managers the Sections of the Society have been increased in size. 
Up to the present, a Board of Managers has consisted of Section Chairman, 
Section Past-Chairman, Section Secretary-Treasurer, and two Managers. In 
view of requests from the Sections, the number of Managers has been increased 
to six, making a total of nine members of the Board. 

PROPOSED AMENDMENTS TO THE BY-LAWS 

At the meeting of the Board of Governors at New York on July 19th, the 
following amendments to the By-Laws were proposed and approved for publica- 
tion in the JOURNAL and subsequent action by the members of the Society in 
meeting at the forthcoming Convention at Hollywood, October 21-25th. Both 
the present wording and the proposed wording are here given: 

BY-LAW XI, SEC. 4, OFFICERS 

Present Wording. Each Section shall nominate and elect a chairman, two 
managers, and a secretary-treasurer. The Section chairman shall. . . . 

Proposed Wording. The officers of each Section shall be a chairman, six 
managers, and a secretary-treasurer. The Section chairmen shall automatically 
become members of the Board of Governors of the General Society, and continue 
in that position for the duration of then* terms as chairmen of the local sections. 
All Section officers shall hold office for one year, or until their successors are 
chosen. 

BY-LAW XI, SEC. 5, BOARD OF MANAGERS 

Present Wording. The Board of Managers shall consist of the Section chair- 
man, the Section past-chairman, the Section secretary-treasurer, and two Active, 
Fellow, or Honorary members, one of which last named shall be elected for a two- 
year term, and one for one year, and then one for two years each year thereafter. 
At the discretion of the Board of Governors, and with their written approval, 
this list of officers may be extended. 



324 SOCIETY ANNOUNCEMENTS 

Proposed Wording. The Board of Managers shall consist of the Section chair- 
man, the Section past-chairman, the Section secretary-treasurer, and six Active, 
Fellow, or Honorary members. The managers of a Section shall hold office for 
two years, or until their successors are chosen. 

BY-LAW XI, SEC. 6, ELECTIONS 

Present Wording. The officers of a Section shall be Active, Fellow, or Honorary 
members of the General Society. They shall be nominated and elected to sec- 
tional office under the method prescribed under By-Law VII, Sec. 1, for the 
nomination and election of officers of the General Society. The word manager 
shall be substituted for the word governor. All Section officers shall hold office 
for one year, or until their successors are chosen, except the Board of Managers, 
as hereinafter provided. 

Proposed Wording. The officers and managers of a Section shall be Active, 
Fellow, or Honorary members of the General Society. 

Not less than three months prior to the annual Fall Convention of the Society, 
nominations shall be presented to the Board of Managers of the Section by a 
Nominating Committee appointed by the chairman of the Section, consisting 
of seven members, including a chairman. The committee shall be composed of 
the present chairman, the past-chairman, two other members of the Board of 
Managers not up for election, and three other Active, Fellow, or Honorary mem- 
bers of the Section not currently officers or governors of the Section. Nomina- 
tions shall be made by a three-quarters affirmative vote of the total Nominating 
Committee. Such nominations shall be final, unless any nominee is rejected 
by a three-quarters vote of the Board of Managers, and in the event of such re- 
jection the Board of Managers will make its own nomination. 

The remainder of the procedure shall be in accordance with procedures specified 
for the election of officers of the General Society as described in By-Law VII, 
Sec. 1A, the word manager being substituted for the word governor. 



JOURNAL 

OF THE SOCIETY OF 

MOTION PICTURE ENGINEERS 

Volume XXXV October, 1940 

CONTENTS 

Page 

Portable Television Pick-Up Equipment 

G. L. BEERS, O. H. SCHADE, AND R. E. SHELBY 327 

A New Negative Carbon for Low-Amperage High-Intensity 
Trims W. W. LOZIER, D. B. JOY AND R. W. SIMON 349 

Color Theories and the Inter-Society Color Council 

H. P. GAGE 361 

The Theater Standardization Activities of the Research Coun- 
cil of the Academy of Motion Picture Arts and Sciences .... 

J. K. HILLIARD 388 

Improvements in Motion Picture Laboratory Apparatus 

C. E. IVES AND E. W. JENSEN 397 

Technical Notes 

A System for Reduction of 120-Cycle Modulation from A-C 
Operated Exciter Lamps J. R. COONEY 411 

Current Literature 413 

Fall Convention at Hollywood, Calif., October 21-25, 1940 

General 415 

Summaries of Papers 420 

Society Announcements 432 



JOURNAL 

OF THE SOCIETY OF 

MOTION PICTURE ENGINEERS 



SYLVAN HARRIS, EDITOR 

Board of Editors 
J. I. CRABTREE, Chairman 

A. N. GOLDSMITH A. C. HARDY T. E. SHEA 

J. G. FRAYNB L. A. JONES G. E. MATTHEWS 

A. C. DOWNES E. W. KELLOGG 



Subscription to non-members, $8.00 per annum; to members, $5.00 per annum, 
included in their annual membership dues; single copies, $1.00. A discount 
on subscription or single copies of 15 per cent is allowed to accredited agencies. 
Order from the Society of Motion Picture Engineers, Inc., 20th and Northampton 
Sts., Easton, Pa., or Hotel Pennsylvania, New York, N. Y. 
Published monthly at Easton, Pa., by the Society of Motion Picture Engineers. 

Publication Office, 20th & Northampton Sts., Easton, Pa. 
General and Editorial Office, Hotel Pennsylvania, New York, N. Y. 

West Coast Office, Suite 226, Equitable Bldg., Hollywood, Calif. 
Entered as second class matter January 15, 1930, at the Post Office at Easton, 
Pa., under the Act of March 3, 1879. Copyrighted, 1940, by the Society of 
Motion Picture Engineers, Inc. 

Papers appearing in this Journal may be reprinted, abstracted, or abridged 
provided credit is given to the Journal of the Society of Motion Picture Engineers 
and to the author, or authors, of the papers in question. Exact reference as to 
the volume, number, and page of the Journal must be given. The Society is not 
responsible for statements made by authors. 



OFFICERS OF THE SOCIETY 

* President: E. A. WILLIFORD, 30 East 42nd St., New York, N. Y. 

* Past-President: S. K. WOLF, RKO Building, New York, N. Y. 

* Executive Vice-President: N. LEVINSON, Burbank, Calif. 

** Engineering Vice-President : D. E. HYNDMAN, 350 Madison Ave., New York, 
N. Y. 

* Editorial Vice-President: J. I. CRABTREE, Kodak Park, Rochester, N. Y. 

** Financial Vice-President: A. S. DICKINSON, 28 W. 44th St., New York, N. Y. 

* Convention Vice-President: W. C. KUNZMANN, Box 6087, Cleveland, Ohio. 

* Secretary: J. FRANK. JR., 356 W. 44th St., New York, N. Y. 

* Treasurer: R. O. STROCK, 35 11 35th St., Astoria, Long Island, N. Y. 

GOVERNORS 

* M. C. BATSEL, Front and Market Sts., Camden, N. J. 

* J. A. DUBRAY, 1801 Larchmont Ave., Chicago, 111. 
** A. N. GOLDSMITH, 580 Fifth Ave., New York, N. Y. 
** H. GRIFFIN, 90 Gold St., New York, N. Y. 

* P. J. LARSEN, 29 S. Munn Ave., East Orange, N. J. 

* L. L. RYDER, 5451 Marathon St., Hollywood, Calif. 

** A. C. HARDY, Massachusetts Institute of Technology, Cambridge, Mass. 

* H. G. TASKER, 5451 Marathon St., Hollywood, Calif. 

* Term expires December 31, 1940. 
** Term expires December 31, 1841. 



PORTABLE TELEVISION PICK-UP EQUIPMENT * 
G. L. BEERS,** O. H. SCHADE,t AND R. E. SHELBYtt 

Summary. Spot news, athletic events, parades, etc., form an important source of 
television program material. In the spring of 1938 field experiments were started in 
New York City with mobile television pick-up equipment. Two telemobile units were 
used each of which was about the size and shape of a twenty-five passenger bus and 
weighed ten tons. The limitations of these telemobile units are discussed. Light- 
weight television pick-up equipment has recently been developed. The new equipment 
includes a small Iconoscope camera, camera auxiliary, camera control and syn- 
chronizing generator units, and an ultra-high-frequency relay transmitter and re- 
ceiver. Most of the units are about the size of a large suitcase and weigh between 40 
and 70 pounds. Each of the units is described and some of the practical applica- 
tions of the equipment are indicated. 

In the spring of 1938 field experiments were started in New York 
City with mobile television pick-up equipment. Two telemobile 
units were used, one of which contained standard rack-mounted 
equipment for two cameras and the other housed a 159-megacycle, 
300-watt transmitter. Each unit was about the size and shape of a 
twenty-five passenger bus and weighed ten tons. The total power 
required to operate both units was approximately twenty kilowatts. 
Field tests with the mobile units have definitely proved their use- 
fulness in providing entertaining television programs. The size, 
weight, and power requirements of these units, however, have im- 
posed definite restrictions on their use. In order to minimize these 
restrictions light-weight portable television pick-up equipment has 
recently been developed. It is the purpose of this paper to describe 
the several units of this equipment and indicate some of its possible 
applications. 

GENERAL CHARACTERISTICS OF THE EQUIPMENT 

Past experience with all types of television pick-up equipment has 
shown that it is desirable to locate all the control equipment at 
* Presented at the 1940 Spring Meeting at Atlantic City, N. J., and at the 
New York Meeting of the Institute of Radio Engineers, April 3, 1940. 
** RCA Manufacturing Co., Camden, N. J. 
f RCA Radiotron Corp., Harrison, N. J. 
tf National Broadcasting Co., New York, N. Y. 

327 



328 



BEERS, SCHADE, AND SHELBY 



[J. S. M. P. E. 



some central point if effective program supervision with a minimum 
of personnel is to be obtained. It is therefore essential that provision 
be made in portable television pick-up equipment so that long lengths 
of camera cable can be used between the control equipment and the 
cameras. This requirement was responsible, to a considerable ex- 
tent, for the division of the equipment into the several units shown 
in the diagram of Fig. 1. In this diagram the units for a complete 
system with a single camera are outlined by the solid lines. The addi- 
tional units required for a second camera are shown by the dotted 




FIG. 1. Block diagram of complete portable television pick-up 
system. 



lines. The only units that must be duplicated to add a third camera 
are the camera auxiliary and camera control units. The receiver 
shown in the diagram is normally located at or near the main televi- 
sion transmitter and is therefore not a part of the equipment that must 
be transported to the remote pick-up point. 

The equipment is designed to produce synchronizing signals in ac- 
cordance with the RMA standards. All the video-frequency ampli- 
fiers are adjusted to pass a frequency band from 30 cycles to 5 mega- 
cycles. Lengths of camera cable up to 500 feet can be used between 
the camera and camera control equipment so that any two cameras 
can be separated by distances up to 1000 feet. 



Oct., 1940] 



TELEVISION PICK-UP EQUIPMENT 



329 



The equipment operates from any suitable 110- volt, 60-cycle, 
single-phase power supply system. The power consumption for the 
portable equipment with one camera, two cameras, and three cameras 
is 1400, 2000, and 2500 watts, respectively. 




!' t WjM 




FIG. 2. Synchronizing generator shaping unit tube 
side, cover removed. 




FIG. 3. 



Synchronizing generator shaping unit circuit 
component side, cover removed. 



All the units are designed to make the tubes and circuit components 
as accessible as possible. The suitcase type of construction used 
for the camera auxiliary, camera control, master control, and three 
synchronizing generator units is illustrated by Figs. 2 and 3. These 
photographs show both sides of the synchronizing generator shaping 



330 BEERS, SCHADE, AND SHELBY [j. s. M. p. E. 

unit. The accessibility of the tubes on one side of the unit and the 
circuit components on the other is clearly illustrated. The central 
chassis portion of the unit is welded to the outside case to form a 
rigid unit. A view of the complete unit with the side covers in place 
is shown in Fig. 4. The overall dimensions of the suitcase type units 
are 8 X 15 X 25 inches, and their weights vary between 45 and 72 
pounds. The camera weighs 28 pounds and its tripod 30. The 
weights of the transmitter and its power supply unit are 60 and 190 
pounds. The total weights of the portable pick-up equipment, less 




FIG. 4. Synchronizing generator shaping unit with 
covers in place. 

interconnecting cables for one, two, and three cameras, are 550, 850, 
and 1050 pounds, respectively. These weights can each be 
reduced by 250 pounds when the equipment is used at locations from 
which the television signals can be sent by coaxial cable to the main 
transmitter. The camera cable used with the equipment weighs 
approximately 0.6 pound per foot. If 500-foot cables are used with 
each of three cameras, the total weight of these cables is approxi- 
mately the same as the total weight of the equipment units. The 
functions of the individual units are discussed in the following sec- 
tions. 

Camera. In order to keep the camera dimensions as small as 
possible the camera was designed to use the new 4 x /2-inch Iconoscope 



Oct., 1940] 



TELEVISION PICK-UP EQUIPMENT 



331 



Development work on small Iconoscopes has been in progress for 
several years. As the dimensions of an Iconoscope are made smaller, 
with a corresponding reduction in the mosaic area, a loss in resolution 
and sensitivity is normally expected. A new gun structure that has 
recently been developed has made it possible to obtain adequate 
resolution from the 4V2-inch Iconoscope. Tests on this tube have 




FIG. 5. 



Portable television camera on 
tripod. 



shown also that its operating sensitivity when using a lens of a given 
aperture is substantially the same as that of the standard Iconoscope. 
This unexpected sensitivity is attributed to the smaller spacing be- 
tween the several tube elements, resulting in a more efficient collec- 
tion of the secondary electrons. This increase in the electron-collect- 
ing efficiency enables the tube to be operated at a higher average 
beam current for a given ratio of signal to dark spot voltage. 

Fig. 5 is a photograph of the camera mounted on a standard motion 
picture tripod, and shows the wire frame view-finder used by the 



332 



BEERS, SCHADE, AND SHELBY [j. s. M. P. E. 




FIG. 6. Right side of portable television camera, cover 
removed. 




FIG. 7. Left side of portable television camera, cover 
removed. 



Oct., 1940] TELEVISION PICK-UP EQUIPMENT 333 

cameraman to keep the scene to be televised within the field of the 
camera. Focusing is done remotely by observing the picture on the 
Kinescope in the camera control unit. A selsyn motor at the camera- 
control unit is used to operate a similar motor in the camera which in 
turn drives the lens carriage. 

The internal construction of the camera is shown by the photo- 
graphs in Figs. 6 and 7. The focusing motor is housed within the 
rectangular shield which is visible in the lower right-hand corner 




FIG. 8. Portable television camera lens mount- 
ing. 

of Fig. 6. The two-stage preamplifier, which can be seen in Fig. 7, 
is used to raise the picture signals derived from the Iconoscope to a 
satisfactory level for transmission over a short length of coaxial cable 
to the camera auxiliary unit. The Iconoscope with its deflection 
yoke, the lens carriage, and the two shielded bias lights, which are 
mounted in back of the Iconoscope, are all clearly shown in this 
photograph. 

Fig. 8 shows the lens mounting arrangement. Lenses are inter- 
changed by loosening the four thumbscrews shown in the photograph 
and then rotating the lens mounting slightly in a counter-clockwise 



334 



BEERS, SCHADE, AND SHELBY 



[J. S. M. p. E. 



direction. The complete lens mounting assembly can then be re- 
moved by pulling it forward. Another lens is attached to the camera 
by reversing the procedure. 




FIG. 9. 



Camera auxiliary unit tube side, cover re- 
moved. 







FIG. 10. 



Camera auxiliary unit circuit component side, 
cover removed. 



Camera Auxiliary Unit. The problem of obtaining satisfactory 
deflection of the Iconoscope beam when a long length of camera cable 
is used is greatly simplified when the horizontal deflection power is 
developed in or near the camera. The use of a camera auxiliary 
unit makes it possible to meet this requirement and at the same time 
keep the dimensions and weight of the camera as small as possible. 



Oct., 1940] 



TELEVISION PICK-UP EQUIPMENT 



335 



In addition to the horizontal deflection circuits the camera auxiliary 
unit contains a 4-stage video-frequency amplifier, Iconoscope blank- 
ing and protection circuits, and a power-supply rectifier. This unit 
is connected to the camera through an 8-foot length of camera cable 
and is usually located between the legs of the camera tripod. 

The video-frequency amplifier, which contains both a high-fre- 
quency peaking and low-frequency losing circuit, is used to raise the 
video-frequency signal from the preamplifier in the camera to a suffi- 
cient level so that a satisfactory signal-to-noise ratio is obtained at 
the receiving end of a 500-foot length of camera cable. This ampli- 



AXIAL CABLE TO MASTER YQKE 

NTROC OR TRANSMITTER t 




FIG. 11. Block diagram of camera control unit. 



fier is assembled as a complete unit on a small chassis which is flexibly 
mounted in an opening in the main chassis of the camera auxiliary 
unit. The construction of the amplifier and the method of mounting 
are illustrated in Figs. 9 and 10. It will be noted that this construc- 
tion maintains the general arrangement of having all the tubes ac- 
cessible from one side of the unit and the circuit components and 
wiring accessible from the other. 

The voltage wave developed across the Iconoscope deflection 
yoke is used to produce a vertical Iconoscope blanking pulse. A pro- 
tective circuit is provided by which the grid of the Iconoscope re- 
ceives a high negative bias if for any reason the deflection of the Icono- 
scope beam is interrupted, thereby preventing damage to the Icono- 
scope mosaic. Horizontal sawtooth waves produced in the camera- 



336 



BEERS, SCHADE, AND SHELBY 



[J. S. M. P. E. 



control unit are transmitted to the camera auxiliary unit over a 
flexible coaxial line included in the main camera cable. These waves 
are amplified by a two-stage amplifier in this unit and fed to the 




FIG. 12. Camera control unit tube side, cover re- 
moved. 




FIG. 13. 



Camera control unit circuit component side, 
cover removed. 



Iconoscope deflecting yoke through a step-down transformer. The 
power-supply rectifier in the camera auxiliary unit supplies anode 
potentials to all the tubes in both this unit and the camera. A 15- 



Oct., 1940] 



TELEVISION PICK-UP EQUIPMENT 



337 



conductor rubber-covered camera cable is used to provide the elec- 
trical connections between the camera auxiliary and camera con- 
trol units. The outside diameter of this cable is slightly under one 
inch. As previously stated, lengths of camera cable up to 500 feet can 
be used between the camera auxiliary and camera control units. 

Camera Control Unit. The camera control unit is normally the 
central control point at which all the operating adjustments are made 
while the equipment is in use. The several functions of this unit are 




FIG. 14. Camera control unit front view. 

indicated by Fig. 11. The video-frequency system shown in this 
diagram amplifies the video-frequency signals received over the cam- 
era cable from the camera auxiliary unit. Blanking and shading 
signals are inserted in this portion of the system. The shading sig- 
nals used are sawtooth and parabolic waves at both line and field 
frequencies. Controls are provided for varying both the amplitude 
and phase of these signals. In case only a single camera is used syn- 
chronizing signals can be inserted in the video-frequency system of 
the camera control unit. Suitable signal potentials are supplied to the 
7-inch Kinescope which is used to monitor the picture and the 2-inch 



338 BEERS, SCHADE, AND SHELBY [j. s. M. P. E. 

oscilloscope which is used to observe the wave-shapes of the picture 
signals. The video-frequency system is also designed to feed a 2- volt 
peak-to-peak signal to a 75-ohm coaxial cable. Controls are pro- 
vided for varying the video-frequency gain and the amplitude of the 
Kinescope blanking signals. 

In the deflection system line and field frequency impulses received 
from the synchronizing generator are used to produce sawtooth 
waves which are supplied to the Iconoscope, Kinescope, and oscillo- 
scope. Provision is made in the synchronizing generator delay unit 
for delaying the Kinescope horizontal deflection impulses with respect 
to the Iconoscope impulses. Facilities are included in the camera- 
control unit for keystoning the horizontal deflection of the Icono- 
scope. A switch is provided so that horizontal deflection of the 
oscilloscope at either line or field frequency can be obtained. Kine- 
scope and Iconoscope width, height, and centering controls are 
included. The line and field frequency sawtooth waves produced in 
the deflection system are also used as shading signals in the video- 
frequency system. The power-supply system includes a high-volt- 
age rectifier for supplying anode potentials to the Iconoscope and 
Kinescope. A low- voltage rectifier is used to supply anode potentials 
to all the other tubes in the camera control unit. Focus and bias 
controls for the Kinescope and Iconoscope are included in this portion 
of the system. 

Figs. 12 and 13 show both sides of the camera control unit with the 
side covers removed. The front of this unit showing the Kinescope, 
oscilloscope, and the several control knobs is illustrated by the photo- 
graph in Fig. 14. A metal cover is supplied which protects these tubes 
and knobs when the equipment is not in use. 

Master Control Unit. When more than one camera is used to tele- 
vise a desired scene some means must be provided for switching from 
one camera to another and for monitoring the "on the air" picture. 
In the portable pick-up equipment these requirements are filled by 
the master control unit. Fig. 15 shows the several functions of this 
unit. The video-frequency system amplifies the signals received 
from the camera control unit and supplies them to the Kinescope 
and oscilloscope. Synchronizing signals are normally inserted in the 
video-frequency system of the master control unit. The line am- 
plifier in this unit is designed to provide a 4- volt peak-to-peak signal 
across a 75-ohm line. A separate 75-ohm output circuit is included 
which can be used to feed an additional monitor unit. The video- 



Oct., 1940] 



TELEVISION PiCK-Up EQUIPMENT 



339 



frequency system is provided with an interlocked switching arrange- 
ment by which any one of four input signals can be selected, ampli- 
fied, monitored, and fed to the outgoing line. Indicator lights on 
both the master control unit, each camera control unit, and camera 
show which camera is "on the air." 

The deflection system for the master control unit employs synchro- 
nizing and deflection circuits essentially the same as those used in 
television receivers. The picture observed on the Kinescope in the 
master control unit is therefore an indication of the performance to 
be expected at the receiving locations. 



SYNCH. INPUT 




FIG. 15. Block diagram of master control unit. 

The low-voltage and high-voltage rectifiers used in the master 
control unit are similar to those included in the camera control unit. 
Fig. 16 is a front view of the master control unit and shows the switch- 
ing and indicator light arrangement. 

Synchronizing Generator. The portable synchronizing generator 
is designed to produce pulses in accordance with the standards of the 
Radio Manufacturers Association. The synchronizing generator is 
divided into three units: the pulse unit, the shaping unit, and the 
delay unit. 

Pulse Unit. The pulse unit contains an electromechanical pulse 
generator for producing 26,460- and 60-cycle pulses. This type of 
pulse generator was used because it gave the desired electrical char- 
acteristics with a minimum of equipment. This generator consists 
of a brass disk having 441 peripheral teeth and rotated by a 3600- 
rpm synchronous motor. This disk revolves inside a stationary 



340 



BEERS, SCHADE, AND SHELBY 



[J. S. M. P. E. 



brass ring having 441 teeth on its inner circumference. The clear- 
ance between the teeth on the rotor and stator is approximately 0.012 
inch. A single radial fin is used on the rotating disk in conjunction 
with a similar stationary fin to produce the 60-cycle pulses. D-c 
polarizing voltage is applied between the stators and the rotating 
disk through resistors. The current variations through the resistors 
in accordance with the changes in capacity produce the desired volt- 




FIG. 16. Master control unit front view. 



age pulses. The use of a large number of teeth on both rotor and 
stator minimizes the effect of inaccuracies in the width of the teeth 
and the spacing between them, since each pulse is produced by the 
average change in capacity caused by each of the 441 teeth on the 
rotor and stator. In addition to the pulse generator the pulse unit 
contains tubes and associated circuits for shaping the pulses and for 
obtaining pulses at line frequency by selecting every other one of 
the 26,460 pulses. A power-supply rectifier to provide anode po- 
tentials for the complete synchronizing generator is also included 
in the pulse unit. Fig. 17 shows the tube side of the pulse unit. The 



Oct., 1940] TELEVISION PICK-UP EQUIPMENT 341 

pulse generator is shown in the lower left-hand corner of the figure. 
The rotor and stator are completely surrounded by a bakelite housing. 
Shaping Unit. The shaping unit receives 60, 13,230, and 26,460- 
cycle pulses from the pulse unit. Four sets of pulses are provided by 
the shaping unit as follows : 

(1) Iconoscope horizontal driving pulses 
(2} Iconoscope vertical driving pulses 
(5) Blanking pulses 
(4} Synchronizing pulses 

Although the synchronizing pulses are formed by combinations of 
several pulses the leading edge of each pulse is the leading edge of a 




FIG. 17. Synchronizing generator pulse unit tube side, cover 
removed. 

26,460-cycle pulse. Controls are provided for varying the width 
of the several pulses. Photographs of the shaping unit with the 
side covers removed have been previously shown in Figs. 2 and 3. 
Delay Unit. When two or more cameras are connected to the con- 
trol equipment through cables differing greatly in length, it is neces- 
sary to delay the driving pulses to the camera connected to the 
shortest cable so that the pulses returning to the control equipment 
from this camera correspond in time with those returning from the 
camera connected to the longest cable. The synchronizing generator 
delay unit contains an artificial line which is used to delay the 
driving pulses to any one of three cameras by an amount corre- 



342 



BEERS, SCHADE, AND SHELBY 



[J. S. M. P. E. 



spending to any normal length of camera cable up to 500 feet. Buffer 
tubes are used between the switches and the artificial line so that 
the characteristics of the line are not affected by the various lengths 





FIG. 18. 



Synchronizing generator delay unit tube side, cover 
removed. 




FIG. 19. 



Synchronizing generator delay unit- 
side, cover removed. 



circuit component 



of camera cable. Switch positions are provided for 50, 100, 200, 
300, 400, and 500-foot lengths of cable. Fig. 18 is a photograph of 
the tube side of the delay unit, and shows the switch knobs for varying 



Oct., 1940] 



TELEVISION PICK-UP EQUIPMENT 



343 



the delay for each camera. The photograph shown in Fig. 19 illus- 
trates the construction of the artificial line and the circuit com- 
ponents used with the buffer tubes. The space in the bottom of 
both sides of this unit is used to carry spare tubes. 

Relay Transmitter. One of the requirements of any portable 
pick-up system is that some provision must be made for conveying 




FIG. 20. 



Ultra-high-frequency relay transmitter 
front view. 



the signal from the remote point to the location where it can be 
utilized. The wide frequency band used in television makes this 
problem especially difficult. One obvious solution is of course a 
portable transmitter for relaying the signal from the remote pick-up 
point to a suitable receiving location near the main transmitter. An 
ideal transmitter for this type of work must be reasonably rugged, 
light in weight, and deliver sufficient power to provide a satisfactory 
service range. The ultra-high-frequency television relay transmitter 
was designed to meet these requirements. This transmitter is crystal- 



344 



BEERS, SCHADE, AND SHELBY 



[J. S. M. p. E. 



controlled and will deliver a peak power of 25 watts at any specified 
frequency between 280 and 340 megacycles. The radio-frequency 
portion of the transmitter consists of four stages: crystal oscillator, 
two multiplier stages, and the power-amplifier stage. Two neutralized 
1628 triodes are used in the power amplifier. All the circuits which 
are resonant at carrier frequency are "transmission line circuits." 
All the other r-f circuits are conventional L-C circuits. 



/TV 




FIG. 21. Ultra-high-frequency relay transmitter rear view, 
doors open. 



The video-frequency portion of the transmitter consists of three 
stages adjusted to pass the frequency band between 30 cycles and 
5 megacycles. An input of 2 volts peak-to-peak is sufficient for 
complete grid modulation of the power amplifier stage. The d-c 
component of the video signal is restored in the grid circuit of the 
modulator stage, and d-c coupling is employed between the modulator 
plate and the power-amplifier grids. 



Oct., 1940] TELEVISION PICK-UP EQUIPMENT 345 

The monitoring system in the transmitter consists of a diode recti- 
fier, a video-frequency amplifier, and a 2-inch oscilloscope. Provision 
is made so that the output of the video-frequency amplifier can be 
fed to a master control unit so that the complete picture can be moni- 
tored. 

The transmitter output system is so arranged that either a coaxial 
line or balanced feeder system may be used. Small antennas having 
high directivity are readily obtainable at the transmitter frequency. 
A unidirectional array using eight half-wave elements has given 
a measured power gain of 12 in field tests. 

Fig. 20 is a front view of the transmitter. The overall dimensions 
of this unit are 6 X 24 X 26 inches. The antenna transmission line 




FIG. 22. Ultra-high-frequency relay transmitter power- 
supply unit. 



clamping unit is shown extending from the top of the transmitter 
unit. The monitoring oscilloscope is viewed through the circular 
opening in the upper right-hand corner of the picture. The meters 
at the bottom of the unit indicate the currents in the various tubes. 

The rear view of the transmitter with the doors open is shown in 
Fig. 21. The location of the various circuit components, tubes, and 
transmission lines can be seen in this photograph. 

Transmitter Power-Supply Unit. This unit contains two rectifier 
systems which furnish all the d-c voltage necessary for the operation 
of the transmitter. Fig. 22 shows a view of this unit. 

Relay Receiver. The relay receiver is a superheterodyne designed 
to operate from a 150-ohm antenna transmission line. Coupled fixed- 
tuned "transmission line" circuits are used in the input system of the 



346 BEERS, SCHADE, AND SHELBY [j. S. M. P. E. 

receiver. These circuits are adjusted to pass a frequency band of 12 
megacycles in the range between 280 and 340 megacycles. The 
oscillator circuit is also of the "transmission line" type. The inter- 
mediate-frequency amplifier consists of seven transformer-coupled 
stages. The second detector circuit is d-c coupled to the automatic 
volume-control rectifier, so that the automatic volume-control volt- 
age is proportional to the peak value of the incoming video signal, 
i. e., synchronizing peaks. Provision is made for disconnecting the 
automatic volume control and using manual volume control if de- 
sired. The video-frequency amplifier supplies an output of about 
2 volts peak to peak across a 75-ohm line. Figs. 23 and 24 show the 










3^ ^^^^>/w. 



FIG. 23. Ultra-high-frequency relay receiver front 
view. 



front and rear views of the receiver. The front view of the power 
supply unit is given in Fig. 25. 

PRACTICAL APPLICATIONS OF THE EQUIPMENT 

Television programs have been broadcast as a public service during 
the past year. The telemobile units previously mentioned have been 
used in many "on the scene" pick-ups and these have almost all been 
very popular. The pick-up of many potentially interesting programs 
has been impracticable because of the size, weight, and power require- 
ments of the mobile units. Although the cameras associated with 
these units can be operated at distances up to 500 feet from the unit 
housing the control equipment, this in many instances is not sufficient 
because the control unit can not be placed in an advantageous loca- 



Oct., 1940] TELEVISION PICK-UP EQUIPMENT 347 

tion. The a-c input power, especially the three-phase for the trans- 
mitter unit, has frequently been very difficult to obtain. 

The new "suitcase" type of portable pick-up equipment there- 
fore greatly increases the program potentialities outside the studio. 
The size, weight, power requirements, and flexibility of the equipment 
are such that for the first time program pick-ups aboard airplanes, 
boats, and automobiles in motion are possible. The program 
possibilities that the equipment creates are thus evident, for it is 
obvious that the extension of the television eye to points outside the 




FIG. 24. Ultra-high-frequency relay receiver rear view. 

studio is an even greater boon to television than was the corre- 
sponding extension of the microphone in sound broadcasting. The 
new equipment has recently been used aboard an airplane to pick up 
scenes of New York and transmit them to Radio City for a program 
broadcast from the transmitter in the Empire State Building. 

It is quite possible to carry the complete pick-up apparatus into 
any building, amusement park, theater, etc., in order to televise events 
that are inaccessible to pick-up equipment mounted permanently in 
a truck. The few kilowatts of single-phase a-c power required for the 
entire equipment can be obtained in most locations. 



348 BEERS, SCHADE, AND SHELBY 

Another important application of the new equipment is the televis- 
ing of regular sound broadcast programs in the studios in which they 
are normally presented. Although such use does not provide all the 
flexibility of a studio permanently equipped for television, it does 
permit a very useful extension of pick-up facilities for certain types 
of programs. 

The portability of the transmitter is a great advantage in remote 
pick-up work. In many locations it is necessary to erect an antenna 
on the roof of a building or some other high structure in order to ob- 
tain line-of-sight transmission to the receiving point. In the case of a 
transmitter mounted permanently in a truck, a rather long radio- 
frequency transmission line is required. The problem of adjusting 




FIG. 25. Ultra-high-frequency relay receiver 
power-supply unit. 

such a line to carry television signals without serious reflections is a 
difficult one, even in a permanent installation, and for portable or 
mobile work the difficulties are still greater. The new equipment 
makes it possible to locate the transmitter on the roof or upper floor of 
a building so that a short radio-frequency transmission line can be 
used to the antenna. In this case the transmitter is connected to 
the pick-up equipment by means of a flexible coaxial cable or other 
video-frequency line. The transmission of the video-frequency sig- 
nals over a suitable line presents a considerably less serious problem 
than the transmission of radio-frequency power over a line of equiva- 
lent length. 

Acknowledgments. The authors wish to acknowledge the indi- 
vidual and cooperative efforts of the many engineers who partici- 
pated in the development of this equipment. 



A NEW NEGATIVE CARBON FOR LOW-AMPERAGE 
HIGH-INTENSITY TRIMS* 



W. W. LOZIER, D. B. JOY, AND R. W. SIMON** 



Summary. A new negative carbon is described which makes possible the extension 
to low current and short arc length of the high-intensity direct-current carbon arc with 
copper-coated non-rotating electrodes. Data are given which show that this new 
negative carbon, known as the "Orotip" C carbon, has made feasible combinations 
of carbons and burning conditions which bring about significant improvements in 
the efficiency of production of light from the standpoint of carbon utilization and power 
consumption. This new negative carbon has practically eliminated carbide tipping 
and its undesirable consequences. Results are given which show that most of the 
theaters now using low-intensity carbon arcs have an inadequate level of screen bright- 
ness. It is shown that the new combinations made possible by the "Orotip" C nega- 
tive carbon offer a remedy for this, while at the same time giving a better color quality 
and maintaining a total operating cost no higher, or only slightly higher, than for the 
low-intensity combination. 



Since the non-rotating high-intensity d-c carbon arc was intro- 
duced about six or seven years ago, it has enjoyed widespread ac- 
ceptance and has become standard equipment in a majority of the 
medium-sized theaters. Its simplicity and high efficiency continue 
to be desirable features and its high output of light of snow-white 
color has enabled it to meet the ever more critical demands for an 
adequate level of light of suitable color quality. The rapid growth 
of motion pictures in natural color has greatly accentuated these 
demands. However, while the large and medium-sized theaters 
throughout the country have adopted the high-intensity arc, over 
sixty per cent of the theaters in this country are still using the low- 
intensity arc. In addition to a less desirable quality of light for 
colored motion pictures, many of these theaters are operating with 
a light-intensity falling far below the minimum brightness recom- 
mended for comfortable viewing. 

* Presented at the 1940 Spring Meeting at Atlantic City, N. J. ; received April 
22, 1940. 

** National Carbon Co., Fostoria, Ohio. 

349 



350 LOZIER, JOY, AND SIMON [j. a M. p. E. 

SCREEN BRIGHTNESS IN THEATERS USING LOW-INTENSITY ARCS 

In order to form a. mental picture of the screen brightness now 
being obtained in theaters using low-intensity lamps it is necessary 
to know the amount of light falling on the screen, the reflectivity of 




10 ,, 20 30 

W/&TH - ttET 

FIG. 1. Screen lumens vs. screen width to give 10.5 
foot-lamberts center brightness with 75 per cent screen 
reflectivity and 70 per cent side-to-center screen dis- 
tribution. 



the screen employed, and its size. Reflection characteristics of the 
screen vary considerably, depending on the type and condition of 
the screen; however, in the discussion to follow, 75 per cent reflec- 
tivity for diffusing screens in good condition has been used. 1 The 
Recommended Practice of the SMPE for screen brightness 2 calls for 
7 to 14 foot-lamberts at the center of the screen without film in the 



Oct., 1940] 



A NEW NEGATIVE CARBON 



351 



projector but with the projector shutter running. For purposes of 
this discussion, the average of these recommended extremes, 10.5 
foot-lamberts, will be used. Fig. 1 shows the total lumens necessary 
to illuminate screens of various widths to a central brightness of this 
magnitude. The decrease in brightness from the center to the sides 




\2 14 16 

3CKEEM 



24- 



FIG. 2. Survey of screen widths in 122 theaters using 
low-intensity carbon arcs. 

of the screen has been taken as 30 per cent in calculating these values. 
Had a more uniformly lighted screen been assumed, the lumen values 
would have been higher. 

Tests made in the laboratory and in theaters have indicated that 
low-intensity lamps and optical systems in good condition can 
project approximately 2400 lumens of light to the screen without the 
projector shutter running and without film in the machine. A 90- 



352 LOZIER, JOY, AND SIMON [J. s. M. p. E. 

degree projector shutter reduces this to 1200 lumens, and reference 
to Fig. 1 indicates that this amount of light will give a center bright- 
ness of 10.5 foot-lamberts or more only with screens 12 feet wide or 
less. 

Previous data 3 on screen sizes in use have not segregated the thea- 
ters using low-intensity lamps from those using high-intensity 
lamps. Therefore during 1939 the National Carbon Company made 
a survey of the screen sizes in 122 theaters using low-intensity lamps. 
These theaters were scattered all over the United States, so that it 
is reasonable to believe that the data are representative. The 
results of this survey are given in Fig. 2, which shows both the fre- 
quency distribution and the cumulative total of the different screen 
sizes. The screens range from 11 to 23 L /z feet in width, 85 per cent 
being 18 feet wide or less, while only 5 per cent have a width of 12 
feet or less. Therefore this survey indicates that only 5 per cent of 
the theaters now using low-intensity lamps have sufficient light to 
illuminate their screens to a central brightness of 10.5 foot-lamberts. 
As indicative of the remainder, it should be noted that a screen 18 
feet wide would have a central brightness of only about 4.5 foot- 
lamberts with low-intensity arc illumination. It should be realized 
that these figures throughout are based on favorable conditions of 
light output and screen reflectivity. Where these conditions are not 
maintained the light levels are even lower than those indicated. 

That there is a decided need for a higher level of screen illumination 
in theaters now using low-intensity arc illumination does not require 
further demonstration. 

The most important qualifications demanded of a light-source 
capable of accomplishing the desired result are 

(1) A higher light output than the low-intensity arc 

(2) A satisfactory light quality for the projection of colored motion pictures 
(5) A low cost of operation 

(4) A satisfactory burning performance 

PRESENT "SUPREX" CARBONS 

The sizes of "Suprex" carbons most widely used today are the 
8-mm positive with the 6.5-mm or 7-mm negative carbon and the 
7-mm positive with a 6-mm negative carbon. A 6-mm 5-mm 
"Suprex" trim was introduced along with the larger sizes but did not 
attain appreciable usage because the small size of this light-source 
did not give proper coverage at the aperture with the optical systems 



Oct., 1940] A NEW NEGATIVE CARBON 353 

employed, which were designed primarily for the larger carbons. 
Also this trim gave difficulty from carbide tip formation except when 
burned at the higher currents and consumption rates. 

The 7-mm 6-mm trim, although rated for operation over a cur- 
rent range of from 50 to 42 amperes, when burned below 45 amperes, 
had much the same limitations as the 6-mm 5-mm trim. Con- 
sequently, practically all the usage of "Suprex" carbons has been at 
currents no lower than this value. At this, minimum practical limit 
of 45 amperes, the 7-mm 6-mm "Suprex" trim gives with an//2.5 
optical system approximately 5000 lumens on the projection screen 
without the shutter running or 2500 lumens with a 90-degree shutter. 
This value is approximately twice the maximum attainable under 
favorable conditions with the low-intensity arc. 

EFFECTS OF CARBIDE TIP 

As mentioned above, when the current with the 7-mm 6-mm trim 
is reduced below 45 amperes, or correspondingly when the 6-mm 
5-mm "Suprex" trim is used in the lower part of its operating range, 
a coating of rare earth carbide forms on the negative tip. This car- 
bide tip disintegrates forcibly if present during the striking of the 
arc and causes a shower of sparks. Also when allowed to cool, this 
carbide tip is a poor conductor of electricity and in some cases be- 
comes insulating enough to prevent restriking of the arc. In addi- 
tion, during burning, the carbide tip covers the core of the negative 
carbon, thereby reducing its intended effect of steadying the arc. 
This frequently results in wandering of the arc and unsteady light 
on the screen. Usually the carbide tip on the negative carbon 
builds up over a period of 5 to 10 minutes, thereby changing the 
characteristics of the arc during this formation period. This may 
have the effect of requiring more attention to lamp adjustment 
during the burning of the trim, particularly as regards the position 
of the negative carbon and the adjustment of feeding mechanism. 
It thus became apparent that it would be an achievement of con- 
siderable importance if the formation of the carbide tip on the 
negative carbon could be prevented. 

In the course of the ensuing experimental work the effect on car- 
bide tip of the various characteristics of the negative carbon and 
the burning conditions of the arc were studied. It was found, for 
instance, that carbide tip could be reduced by operating with com- 
paratively long arc lengths and also with high currents, as is the case 



354 



LOZIER, JOY, AND SIMON 



[J. S. M. P. E. 



with the present method of operating "Suprex" carbons. However, 
both high currents and long arc lengths make for high power usage 
and rapid carbon consumption, so that they do not fit in with the 
goal of supplying an economical combination for the small-sized 
theater. 

Experiments also showed that a reduction of the diameter of the 
negative carbon would substantially reduce carbide tip. This step, 
however, would increase the consumption rate of the negative car- 




0.250 



FIG. 3. Carbide tip vs. arc length at different cur- 
rents for 6-mm "National" "Suprex" and "National" 
"Orotip" C negative carbons with 7-mm "National" 
"Suprex" positive carbons. 

bon and so is likewise not in harmony with the object of obtaining 
a carbon trim economical to operate. The solution to the problem 
came as the result of the development of an entirely new negative 
carbon. This new negative carbon is known as the "Orotip" C 
carbon. 

TESTS WITH "OROTIP" C NEGATIVE 

When carbide tip occurs to any considerable extent it forms a 
hemispherical cap over the end of the negative carbon, and in ex- 
perimental tests the extent of the carbide tip has quantitatively been 
gauged by noting the apparent depth of this cap. That the "Orotip" 
C negative carbon has effected a remarkable reduction in carbide 



Oct., 1940] 



A NEW NEGATIVE CARBON 



355 



tip is shown by Fig. 3. Here, the depth of carbide tip on the nega- 
tive carbon is given for both the "Orotip" C and the regular "Sup- 
rex" negative for different arc lengths and arc currents. The amount 
of carbide tip with the "Orotip" C negative under the conditions of 
Fig. 3 is less than 0.01 inch, which is too small to be conveniently 
measured with accuracy. It has therefore been estimated by the 
dashed line in Fig. 3. These results show that to obtain with the 




FIG. 4. Burning characteristics of 7-mm "National" "Suprex" positive 
6-mm "National" Orotip C negative vs. current at constant arc length of 
0.175 inch. 

"Suprex" negative the same degree of freedom from carbide tip as 
with the "Orotip" C negative carbon, the current must be kept 
above 45 amperes or the arc length must be maintained longer than 
0.25 inch, as is usual practice with present simplified high-intensity 
trims. The freedom from carbide tip shown by the "Orotip" C 
carbon has made feasible combinations of carbons and burning con- 
ditions hitherto considered impracticable. As shown in Fig. 3 it is 
possible to operate the "Orotip" C at currents as low as 40 amperes 
and arc lengths as short as 0.15 of an inch, without encountering an 



356 



LOZIER, JOY, AND SIMON 



LF. S. M. p. E. 



undesirable amount of carbide tip. The employment of these low 
currents and short arc lengths brings with it worthwhile improve- 
ments in efficiency which will now be described. 

IMPROVEMENT IN ARC EFFICIENCY 

Using the 7-mm "National" "Suprex" positive with a 6-mm 
"National" "Orotip" C negative carbon, laboratory tests have been 



MOM 



vi^ 




.150 .175 .00 j?25 .250 




.150 .175 .200 .Z?5 50 
A*C 



FIG. 5. Burning characteristics of 7-mm" National "Suprex" positive 
6-mm "National" Orotip C negative vs. arc length at constant current of 40 
amperes. 

made on the various arc characteristics at different currents and arc 
lengths. Fig. 4 shows the results obtained with this trim at a constant 
arc length of 0.175 inch in a lamp having a 7.5 :1 magnification mirror, 
which had approximately the same speed as the//2.5 projection lens 
employed. As shown in Fig. 4 (a), when the current is reduced from 
50 to 40 amperes, the screen light, carbon consumption rate, and the 
arc power all decrease. 

There are two quantities which relate to the efficiency of the arc. 



Oct., 1940] A NEW NEGATIVE CARBON 357 

One of these describes the lumens projected to the screen in terms 
of the electrical power consumed, and the other describes the lumen- 
hours projected to the screen in relation to the amount of positive 
carbon consumed. As shown in Fig. 4(&) the amount of screen lumens 
per arc watt remains essentially constant when the current is reduced 
from 50 to 40 amperes, so there is no change in efficiency of utiliza- 
tion of electrical power. However, this same figure shows a gain of 
40 per cent in the total amount of light-energy obtained from a unit 
length of positive carbon. This light-energy, measured in lumen 
hours per inch of positive carbon consumed, increases from 500 at 50 
amperes to 700 at 40 amperes. This gain in efficiency of carbon 
utilization at the lower current is made practicable by the use of 
the "Orotip" C negative carbon which permits low-current operation 
without appreciable carbide formation. 

Fig. 5 shows the results of tests made with the same lamp and 
optical set-up as described for Fig. 4, but in these latter tests the arc 
current was maintained at 40 amperes and the arc length was varied 
from 0.15 to 0.25 inch. This reveals further important gains in 
efficiency through operation at short arc lengths. One very im- 
portant fact illustrated in Fig. 5 (a) is that the screen light is not al- 
tered by operating at arc lengths as short as 0.15 inch. This feature 
has been recognized for some time 4 but was not practicable to use 
because of the formation of carbide tip at short arc lengths. Fig. 
o(a) shows also that reduction of the arc length from 0.25 to 0.15 
inch results in a decrease of 15 per cent in both carbon consumption 
and arc watts. As shown in Fig. 5(6), this results in a 15 per cent 
improvement in efficiency of utilization of both power and carbon for 
producing screen light. 

To summarize, therefore, it has been shown that the low current 
and short arc length operation made possible by the "Orotip" C 
negative has resulted in a marked improvement in the efficiency of 
production of light from the standpoints of both carbon utilization 
and power consumption. 

The foregoing discussion has pertained chiefly to the 7-mm 6-mm 
trim of carbons. Similarly, the "Orotip" C negative carbon makes 
possible the use of a combination of smaller carbons at low currents 
and short arc lengths without the appreciable formation of carbide 
tip. 

The effects of the characteristics of the power source on the stability 
of the non-rotating high-intensity d-c arc have been fully discussed in 



358 



LOZIER, JOY, AND SIMON 



[J. S. M. P. E. 



>i 9 

a ll!J 



i l j 

5 q 



a* 

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aS t 



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A ^ ^ 

^ ^ ? 
3 . a a 



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a 5* 



no S 
(N ^ 



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to 



Oct., 1940] A NEW NEGATIVE CARBON 359 

a previous article. 4 In that discussion it was shown that a low- 
voltage power source with only a slightly falling volt-ampere curve 
at the arc gave a more stable arc and steadier screen light than a 
high-voltage power source with a large proportion of ballast. Like- 
wise in that earlier paper the stabilizing effect of supplementary 
magnetic flux on the arc was explained. Both these factors, the 
characteristics of the power source and the use of supplementary 
magnetic flux, are necessary to obtain the best stability with the 
arcs just described. 

The feeding mechanism must be capable of feeding the carbons 
uniformly and maintaining the short arc gap between the electrodes. 

With both the 7-mm 6-mm trim and the 6-mm 5-mm trim at 
low currents and short arc lengths, the light-source is smaller than 
is the case with the sizes of carbons and currents ordinarily used in 
"Suprex" lamps. The magnification of the mirror collecting the 
light must be sufficient to cover the motion picture aperture. New 
lamps on the market have taken account of this and are equipped 
with mirrors having the higher magnification ratio. 

THEATER APPLICATION 

Table I shows data on the 6-mm 5-mm and 7-mm 6-mm trims 
using the "Orotip" C negative carbon and also shows comparable 
data on the 12-mm 8-mm low-intensity trim. The screen lumens 
per arc watt for these high-intensity trims are from 2 x /2 to 3 times 
as great as for the low-intensity arc. This is an important feature, 
and contributes to the achievement of a total operating cost with 
these high-intensity trims no higher or only slightly higher than for 
the low-intensity combination despite the fact that they give a much 
greater amount and better color of light. 

The last three columns of Table I show the size of a diffusing screen 
of 75 per cent reflectivity which can be illuminated by these light- 
sources to center brightness values of minimum (7 foot-lamberts), 
mean (10.5 foot-lamberts), and maximum (14 foot-lamberts) recom- 
mended screen brightness. The results of the survey on screen sizes 
shown in Fig. 2 indicate that the low-intensity carbons and lamps 
deliver enough light to furnish desirable screen brightness for only a 
small percentage of the theaters now using this combination. These 
new low-amperage high-intensity 6-mm 5-mm and 7-mm 6-mm 
carbon combinations (together with the regular "Suprex" combina- 
tions for the largest screens) extend to the theaters now using low- 



360 LOZIER, JOY, AND SIMON . 

intensity arcs a practicable means of increasing their screen bright- 
ness to the recommended range and, in addition, give them the same 
desirable color quality of light as the theaters now using the high- 
intensity carbon combinations. 

REFERENCES 

1 COOK, A. A. : "A Review of Projector and Screen Characteristics and Their 
Effects upon Screen Brightness," J. Soc. Mot. Pict. Eng., XXVI (May, 1936), 
p. 529. 

2 "Revisions of S.M.P.E. Standards Proposed for Adoption by the Society," 
/. Soc. Mot. Pict. Eng., XXX (Mar., 1938), p. 257. 

3 "Report of the Projection Practice Committee," J. Soc. Mot. Pict. Eng., XXX 
(June, 1938), p. 645. 

4 JOY, D. B., AND GEIB, E. R. : "The Non-Rotating High-Intensity D-C Arc 
for Projection," /. Soc. Mot. Pict. Eng., XXIV (Jan., 1935), p. 49. 

DISCUSSION 

MR. EDWARDS : If we maintain a closer arc with the new "Orotip" C, with conse- 
quently less cost per lumen, then why not increase the size to 8-mm, 60 amperes? 

MR. WILLIFORD: All the improvements can not come out at once. We are 
aware of the industry's desire for greater screen illumination, and have been 
working toward that goal for many years. Intensities have steadily been going 
up. The question of screen light standards has been raised, and the Society has 
been loath to recommend the standards that we think we ought to have until 
we have optical systems, light-sources, and screens that will give us those stand- 
ards. There is no reason why everyone can not today have 10 foot-candles on his 
screen. 

MR. RICHARDSON: Provided the screen width does not exceed 18 feet. 

MR. WILLIFORD : He can have it, even so. With developments now under way 
he can go to higher intensities on any screen. It has been a matter of development 
in various channels, including the matter of lens surfaces. With improvements 
in optical systems, screens, and light-sources we are making it possible to get 
the levels of screen illumination the industry believes it should have. I can 
not promise how soon some of these later developments will enter the larger 
theaters, but they are definitely in the offing, and the results today are exceed- 
ingly promising. 

MR. GRIFFIN: The Standards Committee has already revised the previously 
recommended screen brightness, I believe. 

MR. JOY: The recommended practice at the present time is 7 to 14 foot- 
lamberts at the center of the screen. That means, in terms of foot-candles, 
with a 75 per cent reflection factor, about 9 to 18 foot-candles. For an average 
of, say, 10 foot-candles, we should have about 12 or 13 at the center and falling 
off toward the edges. 

MR. McAuLEY : If we take into account the increased projector shutter speeds ; 
the use of 70-degree shutters instead of 90-degree; the widespread use of high- 
intensity arcs instead of low-intensity or any of the neutral-cored carbons; the 
increased efficiency of the optical systems that is keeping pace pretty well with 
the demand that colored pictures have created for increased illumination. 



COLOR THEORIES AND THE INTER-SOCIETY 
COLOR COUNCIL* 



H. P. GAGE' 



Summary. Thanks to intensified study of color by scientists of the National 
Bureau of Standards, of the Agricultural Marketing Service of the U. S. Department 
of Agriculture, of the Committees of the American Association of Railways, glass 
manufacturers, dye manufacturers, paint and ink manufacturers, the American 
Pharmaceutical Association, and photographic manufacturers and the stimulation 
of the motion picture industry, the theories of color have been put in shape and tied 
together with extensive data on the color vision of many observers so that a workable 
engineering evaluation of colors, a scientific system of naming them, and practical 
means of producing them to exact specification is now available and is ripe for presen- 
tation not only to learned societies but to the general public. 

Colored lights are subject to spectrophotometric measurement and by means of the 
ICI (International Commission on Illumination) data can be interpreted in terms of 
luminosity and the x and y coordinates (or map) defining chromaticity. 

In these terms are being defined the color limits for railway signal colors, also all 
standard Atlases of Color such as the Maertz & Paul Dictionary of Color, the Munsell 
Book of Color, and, it is hoped, the next standard set of colors of the Color Card As- 
sociation of the U. S. used by all manufacturers of clothing and other things in which 
standardization of manufacture in spite of rapid changing styles is an economic 
necessity. 

The next edition of the Pharmacopoeia and of the National Formulary, sponsored 
by the American Pharmaceutical Association, will use the system of color names de- 
veloped and recommended by the Inter-Society Color Council in cooperation with the 
National Bureau of Standards to describe the normal appearance of all drugs and 
chemicals. A shorthand method of describing the spectrophotometric analysis of 
color filters for theater spot and floodlights in the form of a seven digit number has been 
devised for commercial specification of this material. 

The Inter-Society Color Council is made up of 74 delegates appointed by 11 mem- 
ber societies, and 67 individual members. It functions as a joint committee on color 
of the member societies favored with advice of the individual members. The 
Council issues News Letters in mimeograph form to its members. They contain 
information of progress in color work, notices of important color publications, the 
activities of the Color Council and notices of its planned meetings. The Council 
sponsors meetings with the member societies on the subject of color. Such joint meet- 
ings have been held with the Optical Society of America, the Technical Association of 

* Presented at the 1940 Spring Meeting at Atlantic City, N. J. ; received June 
14, 1940. 
** Coming Glass Works, Corning, N. Y. 

361 



362 H. P. GAGE [j. s. M. p. E. 

the Pulp & Paper Industry (T.A.P.P. /.), and the American Psychological Associa- 
tion. A joint technical session on color will be held at the annual convention of the Il- 
luminating Engineering Society this fall and also with the American Society for Test- 
ing Materials at its 1941 spring meeting to be held in Washington. 

The Society of Motion Picture Engineers has become a member of 
the Intersociety Color Council, and has appointed as its three voting 
delegates to the Council Messrs. R. M. Evans, Chairman, G. F. Rack- 
ett, and T. Bowditch. 

It is fitting that the Society of Motion Picture Engineers do this as 
the exhibition of motion pictures has from its rather early days used 
color as far as possible to enhance its artistic appeal. The hand- 
colored French films were, as I remember them, as beautiful as any 
now produced by the modern processes, but made at a cost which 
would be considered prohibitive. About 1910 when I first became a 
serious student of motion pictures, my father and I were given a well 
worn copy of a colored film to experiment with, so that color in films 
can hardly be considered new. The tinting and toning of films were 
frequently resorted to and the lurid colors of fire scenes were well 
known. Sound also had been applied as a curiosity by synchronized 
records. We do all these things now in immeasurably greater volume, 
and, we believe, with greater skill but by methods already outlined 
by the pioneers. 

For the outline of the theories of color vision we go back to Thomas 
Young 1 who proposed that three primary sensations of the eye ac- 
counted for all the colors we see; to Clerk Maxwell who proved this 
to be the case by projecting simultaneously on the screen three- 
colored pictures taken with three color niters, red, green, and blue, 
thereby producing a recognizable reproduction of colored objects. 
The exact behavior of the eye to colors was outlined by Helmholtz 
and studied by Konig and Dieterici. 2 It is to the late Frederick E. 
Ives, 3 for a long time a member of the Society and now on our Honor 
Roll, that we owe the methods, first, of halftone engravings so uni- 
versally used in all printed illustrations, and later of demonstrations 
of methods of three-color photography, which he greatly improved 
with the availability of color-sensitive emulsions. He also developed 
methods of producing colored motion picture films. His work in this 
field stimulated others and greatly accelerated the attainment of the 
present level of achievements in color. His son, Dr. Herbert E. Ives, 
an accomplished student in this field, has demonstrated some of the 
early methods of television to this Society. 4 Of the achievements of 



Oct., 1940] COLOR THEORIES 363 

our fellow members, Dr. C. E. K. Mees and Dr. L. A. Jones, we are 
all aware. Dr. L. T. Troland, who at one time was a member of this 
Society and before his death was connected with the Technicolor 
Corporation, was a deep student of the psychology of color, and was 
the author, after due collaboration with others, of the 1920-21 
Colorimetry Report of the Optical Society of America, 2 which is the 
cornerstone upon which is founded the modern scientific study of 
color. Our Society has listened to reports on color by Dr. K. S. 
Gibson, 6 of the Colorimetry Division of the National Bureau of 
Standards and by Dr. D. B. Judd, 6 also of the same Division. Both 
papers, incidentally, received the Journal Award of the Society in 
their respective years. 7 ' 8 

Of the members of our Society who are also members of the 
Colorimetry Committee of the Optical Society we find Dr. L. A. 
Jones, Chairman, Dr. H. P. Gage, and Prof. A. C. Hardy. 

These members, in addition, are already delegates to the Inter- 
society Color Council, and represent either the Optical Society of 
America or the Illuminating Engineering Society. Besides these of 
our members we find as a delegate to the Council Mr. W. F. Little. 

I hope I have indicated how intimately some of our members have 
been identified with the study of color. Before finishing the discus- 
sion of the Intersociety Color Council and its activities I wish to say 
a word about color theories and how they may be worked into the 
practical problems of the motion picture engineer. 

As has already been pointed out, three primary colors, or sensations 
suitably combined, are sufficient to account for all the colors we can 
perceive. Demonstrations have repeatedly been presented to this 
Society to illustrate the theory of color mixture and to demonstrate 
that one and the same theory serves to clarify both the additive and 
the subtractive processes for the projection of colored pictures. An 
excellent presentation of this subject was recently published by Dr. 
D. L. MacAdam; 9 - 10 also by J. A. C. Yule. 11 

When three projectors are used, one of which produces a red 
field, one a green field, the other a blue field in properly balanced 
amounts, all three projecting slightly different pictures of the same 
subject, we find the following phenomena: Before the three pro- 
jected spots are brought into register, we see red, green, and blue 
(Fig. 1) areas. Where the red and green overlap we get yellow; 
where the green and blue overlap we get blue-green ; where the blue 
and red overlap we get a red-purple, or magenta. Where all three 



364 H. P. GAGE [J. S. M. P. E. 

overlap, if properly balanced, we get white. If, now, each projector 
contains a suitable positive, made from a negative taken through the 
same color-filter, combined images give a life-like representation in 
color of the scene or objects photographed. This is the principle 
used in the Kodacolor process. Instead of presenting the three 
pictures simultaneously they may be presented alternately, and per- 
sistence of vision will blend the colors and action. Flicker enters as a 
complication when using three colors, so two complementary colors, 

GREEN 



YELLOW 




BLUE www\ -- ^>>>>>>>>yy RED 



PURPLE 
Additive Method 

FIG. 1. Illustrating the additive method of color 
mixture. Spots from three separate lanterns are red, 
green, and blue. Where the red and green overlap is 
yellow; where the green and blue overlap is blue-green 
or cyan; where the blue and red overlap is purple or 
magenta; where the three overlay is white. 

red and blue-green, have ordinarily been used, as in the Prizma 
process. 

The subtractive process has frequently been demonstrated by the 
triangular diagram shown in Fig. 3. A lantern-slide in this form was 
constructed by using unmounted Wratten filters, Nos. 44, 32, and 12. 

Across the bottom is a strip of magenta-colored gelatin film. The 
dye in it absorbs only green, transmitting both blue and red. On the 
right side is a yellow film, absorbing only blue, and transmitting red 
and green. On the left is a blue-green film, absorbing only red and 
transmitting blue and green. 



Oct., 1940] 



COLOR THEORIES 



365 



Where two of these strips overlap, as at the left and right corners, 
each strip removes its typical absorption band, and what passes 
through both, is what is left. Thus where the minus green and 
minus red overlap, what remains is blue, which both strips transmit. 
Where the minus green and minus blue overlap, only red is trans- 
mitted. Overlapping minus blue and minus red leave only green, 




FIG. 2. A lantern-slide for producing Fig. 1 is made 
by overlapping three gelatin filters, each cut as indi- 
cated in the right-hand sloping diagonal line. The 
three filters are fastened to a glass slide. On the cover- 
glass is fastened a tinfoil mask of the shape indicated by 
the left-hand sloping lines. While the effect is accom- 
plished by means of the subtractive method, the ap- 
pearance is the same as is secured by the additive 
method. 

and in the center where each film takes its particular toll of white 
light, after removing red, green, and blue, there is nothing left, 
so we get black. This principle is used in the Kodachrome process, 
where three pictures separated by clear gelatin layers have been pro- 
duced in colors essentially like those illustrated in the lantern-slide. 
The phenomena described can be more clearly illustrated by a 
spectrum analysis of the colored gelatins used to make the slide. 
There are many ways of doing this, such as by curves, by photo- 



366 H. P. GAGE [J. S. M. P. E. 

graphs, by observations through a pocket spectroscope, or by pro- 
jection of the spectrum on the screen. The projection of spectra 
often requires such bulky apparatus that one hesitates to transport 
it. For the present purpose it will be demonstrated by a bright-line 
transmission grating prepared by Professor R. W. Wood of the Johns 
Hopkins University. The peculiarity of this grating is that it con- 
centrates most of the energy in one of the first-order spectra. All 
the other orders of spectra are present but are less bright. The 

GREEN 




CYAN /MMMv YELLOW 
(MINUS RED)/M^^MCMINUS BLUE) 



RED 
MAG E N TA 
(MINUS GREEN) 

FIG. 3. The subtraction method of color mixing. 
Three strips of colored gelatins are laid between two 
coverglasses. These are minus red or cyan, minus blue 
or yellow, and minus green or magenta. Where these 
overlap, two by two, is seen red, green, and blue. Where 
all three overlap no light gets through, leaving a black 
triangle. 

gratings with about 5000 lines per inch project this first-order spec- 
trum on the normal picture area. 

First a cardboard with a slit is put into the slide-holder of the 
lantern (Fig. 5). This is made stepwise to produce narrow and wide 
slits. The grating is placed over the projection objective so that on 
the screen, wall, ceiling, and floor are seen all the diffraction spectra. 
The first-order spectrum will fall within the normal picture area on 
the screen. In each spectrum we see three colors, red, green, and 
blue. While by careful scrutiny of narrow strips of this spectrum 
it is possible to isolate orange, yellow, blue-green, and an extreme 



Oct., 1940] 



COLOR THEORIES 



367 



violet, which appears as a slightly bluish red, and while a delicate 
thermopile will detect radiant energy beyond the red, which is known 
as infrared, a photographic plate will show exposure beyond the vio- 
let, which is called ultraviolet. Fluorescent materials will be excited 
and glow in this region. For purposes of our color theory the three 
easily seen bands, red, green, and blue suffice. There is an important 
minority of observers who see colors differently owing to a different 




FIG. 4. Construction of Fig. 3. The three gelatins 
are cut into strips with a triangular extension as illus- 
trated by the right-hand sloping lines. These strips are 
fastened to one coverglass, and a tinfoil mask as indi- 
cated by the left-hand sloping lines is fastened to the 
other glass, giving the appearance shown in Fig. 3. 

type of color-sensitivity of the eye. These are usually treated as 
special cases and their study has added much for the theories of color 
vision. Dr. Judd has given us a paper on this subject. 6 

In front of the lantern objective and grating is now placed a piece 
of didymium glass, which has a narrow absorption band in the yellow 
and other narrow lines in the green. Where the slit is also narrow the 
spectra exhibit these narrow absorption lines. Where the slit is wide, 
the spectra appear brighter but the narrow absorption bands are 
wiped out, This illustrates the importance of a fairly narrow slit in 



368 H. P. GAGE [j. s. M. p. E. 

all spectroscopic analysis, and the eternal conflict between intensity 
and purity or resolution in spectroscopic research. 

A photograph of the projected spectrum can be made as a perma- 
nent record, or some type of sensitive measuring and recording instru- 
ment can be moved across the spectrum to draw a curve such as a 
curve between wavelength and transmission of a filter or reflection 
from a colored surface (Fig. 9). The photoelectric spectrophotometer 
devised by Prof. A. C. Hardy and manufactured by the General 
Electric Company is an outstanding example of how accurately and 
expeditiously such curves can be made for use in analyzing colors. 

If small pieces of the three gelatin filters used in the previous demon- 
stration are placed over parts of the slit, we see (Fig. 6) that corre- 
sponding to the clear parts of the slit there is a complete spectrum, 
but corresponding to those parts of the slit covered by the colored 
gelatins it is apparent that from the complete spectrum of white light, 



Slit 

FIG. 5. Slit having various openings, cut from card- 
board. This should be made to appear in the lower 
portion of the picture area. 

the blue-green gelatin (No. 44) has removed the red, the magenta 
(No. 32) has removed the green, and the yellow (No. 12) has removed 
the blue. If in front of the slit we use the same gelatins and overlap 
them a little, we see the same phenomena as illustrated in the (Fig. 7) 
triangle slide: namely, in the overlapping parts there is transmitted 
only blue, red, or green. 

For black-and-white illustrations photographs made with the 
wedge spectrograph have been used. These are shown in Dr. Mees' 
book, "An Atlas of Absorption Spectra" 12 and the Eastman pam- 
phlet 13 on Wratten light-filters. The instrument is well adapted to 
illustrate the spectral regions to which emulsions are sensitive. 

With the Hardy spectrophotometer now available, most of such 
data can be presented in curve form and this seems to be (Fig. 9) 
preferred by most people. 

INTERPRETATION OF SPECTROPHOTOMETRIC CURVES 

Colored lights are subject to spectrophotometric measurement and 
by means of the ICI (International Commission on Illumination) 



Oct., 1940] 



COLOR THEORIES 



369 



data can be interpreted in terms of luminosity and the x, y coordi- 
nates (or map) denning chromaticity. It is to be clearly understood 
that not only must the spectral transmission or reflection of the filter 
or colored object be considered but also the spectral emission of the 
original light-source. To give a definite place on the diagram to a 
color-filter one must assume a definite light-source. The color-mix- 
ture diagram may be regarded as a map on which any color may be 




RED 
CYAN 



-GREEN 
MAGENTA 



-BLUE 
-YELLOW 




FIG. 6. Lantern-slide with slit, which may be cut in 
tinfoil, over which are placed the gelatin niters. When 
the bright-line diffraction grating of 5000 lines per inch 
is placed over the projection protective, the first-order 
spectrum should appear within the picture area. The 
black spaces indicate the absorbed region of the spectrum. 

represented by its position, and this position compared with the 
positions of other colors will give an idea as to the degree of similarity 
of the respective colors and to the way in which they differ. In the 
case of a geographic map the locations of cities, mountains, and rivers 
are designated by their coordinates, known as latitude and longitude, 
whereby these locations can be placed properly on the map and their 
relation to each other illustrated. There are several types of maps, 
such as the spherical type or globe ; the flat representations of a globe, 
such as Mercator's projection, with its enormous distortion of the 



370 



H. P. GAGE 



[J. S. M. P. E. 



size of the polar regions, notably Alaska and Greenland; and the 
types in which areas are correct but angular distortion occurs. In all 
cases, however, a web of latitude and longitude lines is first drawn 
and the geographic features are located by their measured co- 
ordinates. The original determination of the coordinates is a tech- 
nical matter well known in principle by astronomers, navigators, and 
surveyors. 




MINUS MINUS 


GRE 


.EN BU 


JE 


MINUS 




MINUS 


RED 




RED 


J 




i 




Wtiti. 


v'X^^vSvsSSl 

^ s " s\\\\V 




n 


i 


////j ' ' i ' ' * 


V " V S | V V \\X\N. 


xxxxx 


/////i 




W$m 


I!!!! 


$$$! 


W//. 



FIG. 7. Slit in front of which have been placed over- 
lapping color-filters. Where two filters overlap only the 
color transmitted by both will show in the spectrum. 



With the ICI mixture diagram and coordinate system here illus- 
trated, the coordinates are designated by x and y. The determina- 
tion of the values of x and y of a given color for the ICI Standard 
Observer is again a technical matter. No simple meaning can be 
given to values of x and y, and until the whole process of color analy- 
sis has been worked through and several other methods of color repre- 
sentation have been studied, the full advantages of this particular 
ICI system can not be appreciated. As in the various flat representa- 
tions of the globe, so in this color map there is considerable distortion. 
The diagram does, however, illustrate the relation of the different 



Oct., 1940] COLOR THEORIES 371 

colors to each other so that this relationship may be made apparent to 
anyone. 

To describe the attributes of color four technical terms are used 
and the meanings of these terms must be clearly understood before 
one can make much progress in understanding the subject or in read- 
ing the technical literature. These terms are: 2 

Brilliance. This refers to the intensity of the luminous sensation 
produced. The difference between the appearance of a bright light 
and a dim light is a brilliance difference. (Lightness is the word that 
applies to the black-and-white series of surface colors.) 

Hue. The hue of a color not neutral (gray) is the attribute that 
permits it to be classed as reddish, yellowish, greenish, bluish, etc. 




FIG. 8. Appearance of photograph made with wedge 
spectrograph. The short- wavelength end is limited by 
the transmission of the instrument. The long- wavelength 
end and the uneven top are produced by the limit of 
light-sensitivity of the emulsion. 

Saturation. This is the attribute of all colors possessing hue, 
which determines then- degree of difference from neutral (gray). 

Chromaticity. This term is used to designate the properties of 
color not connected with brilliance; that is, it combines the attributes 
of hue and saturation. It is this property of color that is illustrated 
by the diagram. 

The element of saturation is shown by the distance from the white 
point of the diagram near its center. It will be observed that those 
colors which are closest to the center of the diagram appear pale or 
washed out. They differ but little from white and are said to have low 
saturation. 

Those colors farthest from the center appear most vivid and are 
said to have high saturation. The pure colors of the spectrum have 
the greatest possible saturation for a given hue. It will be noted, 
however, that the most vivid yellows and greens nearest the spec- 
trum line are not as saturated as are the extreme blue and red. 



372 



H. P. GAGE 



[J. S. M. P. E. 



Hue is illustrated by the direction from the center of the diagram 
in which the color is to be found. In one method of color specification 
the hue is defined as the wavelength of the spectrum which the color 
most nearly resembles. 



I 



/TV 



20 40 60 8O 500 20 40 60 80 600 20 4O 60 80 70O 
WAVELENGTH IN MIUUMiCRONS 



FIG. 9. Spectral curves produced by the Hardy spectro- 
photometer for the three filters described. 

(1) Wratten filter No. 12, minus blue or yellow. 

(2) Wratten filter No. 32, minus green or magenta. 
(5) Wratten filter No. 44, minus red or cyan. 



This serves excellently for red, yellow, and blue signal colors which 
lie close to the spectrum line. For the greens, none of which 
lie near the spectrum, considerable difficulty is encountered with 
such a specification, as these colors do not closely resemble any por- 
tion of the pure spectrum. 



Oct., 1940] 



COLOR THEORIES 



373 



Measurement of color, or, more properly, measurement of the color 
stimulus, depends upon three factors: 

(1) A knowledge of the light-source under which the colored ob- 
jects are viewed. The two general types of illuminants most often 
used are: 

(a) Daylight. For this the spectral energy distribution is usually 
assumed as that given in the ICI tables for illuminant C. 




o .1 

FIG. 10. Color-mixture diagram in accordance with 
the 1931 ICI Standard Observer and Coordinate System. 
A copy of this diagram with colored glasses inserted in 
the openings indicated was prepared for demonstra- 
tion at the 1939-1940 New York World's Fair. 

(b) Artificial light. The distribution is usually assumed to be 
that of a complete radiator or black body at 2848K and is called 
ICI illuminant A. This corresponds to a gas-filled tungsten lamp of 
moderate size operated at rated voltage. Other special illuminants 
can be used provided their spectral distribution is known. 

(2) The transmission of colored glasses or the reflectance of colored 
objects for the different portions of the spectrum. 

(3) The sensitivity of the observer's eye for the different spectral 
regions. This differs for each individual. A general average for a 



374 H. P. GAGE [j. s. M. p. E. 

reasonable number of normal observers was made after considerable 
research and the results recorded in tables for the ICI Standard Ob- 
server. Observers obviously color-blind were excluded from this 
general average but have received considerable study as interesting 
special cases contributing to our knowledge of color vision. 

The color vision of the Standard Observer is defined in a table giv- 
ing three values for each wavelength in the spectrum, designated as 
x, y, and z. Values of y by themselves indicate also the relative 
luminosity of the various parts of the equal-energy spectrum, the 
most luminous portion being at a wavelength of 555 mn. This func- 
tion is sometimes called the sensitivity curve of the eye; but taken 
alone refers only to the brilliance aspect of color. The values of x 
and z are in the same proportions compared to y as are the x and z 
values compared to y for the given wavelength in the spectrum. 

The computations are too involved to be described here, even 
briefly, and, as the entire subject can be found adequately treated 
in any one of the several places given below, reference is made to the 
original literature. 

(1) The official publication of the sensitivity of the eye of the 1931 
ICI Standard Observer is to be found in the Commission Inter- 
nationale de 1'Eclarage, 14 Comptes Rendu des Seances in five resolu- 
tions which officially cover the adoption of the particular values de- 
scribing the ICI (or CIE) Standard Observer. 

Resolution 1 refers to the ICI hypothetical observer to be known 
as the 1931 ICI Standard Observer referring to three homogeneous 
stimuli of wavelengths O.TOOju, 0.546/* (the green mercury line), and 
0.4358ju (the blue mercury line), and expresses the results for the 
Standard Observer in a table. 

Resolution 2 is a description of three standard illuminants: 

(A) a gas-filled lamp operated at a color-temperature of 2848K. 

(B) and (C) are energy distributions corresponding to approximate 
color-temperatures of 4800 K and 6500 K. Values are also given 
in a table which is part of the resolution. 

Resolution 5 covers the ICI coordinate system in which the color- 
sensitivity of the same Standard Observer is expressed in accordance 
with a table which is also included in the specification. 

(2) The first article on the ICI system which includes computa- 
tional forms is by T. Smith and J. Guild, 15 published in the Transac- 
tions of the Optical Society (of England). This article is divided into 
a description of the five resolutions adopted by the International 



Oct., 1940] COLOR THEORIES 375 

Commission on Illumination (ICI) otherwise known as the Commis- 
sion Internationale de 1'Eclarage (CIE). 

(3) Deane B. Judd, 16 "The 1931 ICI Standard Observer and Co- 
ordinate System for Colorimetry." Publication 16 in an American 
journal covering tables for the same ICI Standard Observer, giving 
detailed directions for computing the coordinates x and y for a given 
light-source and a color-filter whose spectral transmission is known. 
It also describes methods of determining the dominant wavelength 
and colorimetric purity when the x and y coordinates are known, and 
describes methods of converting the ICI coordinate system into 
other systems. 

(4) K. S. Gibson and Geraldine K. Walker, 17 Signal Section Pro- 
ceedings, American Railway Association : This is one of a series of 
reports illustrating how this system may be used for defining the 
color and transmission of railway signals and the signal glass specifica- 
tions so prepared are intended to serve as a model for all exact color 
specifications. 

(5) Arthur C. Hardy, 18 Handbook of Colorimetry: This book 
contains tables for the luminosity function and the other two sensa- 
tion elements for a greater number of decimals interpolated for each 
millimicron. It also has tables for and illustrates another method of 
calculation from the spectrophotometric curve known as the selected 
ordinate method. Charts are given for determining dominant wave- 
length and purity from the x and y coordinates. 

When the railway signal engineers decided upon the color limits 
within which all colored glass for railway signals had to be supplied, 
the standard limits were accurately defined in terms of the ICI sys- 
tem. 17 The standard atlases of color, such as the Maertz & Paul 
Dictionary of Color, the Munsell Book of Color, and it is expected the 
next standard set of colors of The Textile Color Card Association of 
the United States, will also be defined according to this same ICI 
diagram. 

After studying the 1931 ICI system one would naturally surmise 
that there must have been some fairly useful methods of color speci- 
fication prior to 1931. What were they? One of the most completely 
thought out of these systems resulted from the efforts of Professor 
A. H. Munsell of Massachusetts Normal Art School, an artist but 
also a most versatile individual whose grasp of many subjects re- 
minds us of the diverse activities of Leonardo De Vinci. Munsell 
devised a system of arranging colors in the form of a color solid 



376 H. P. GAGE [j. s. M. P. E. 

whose study as received at third or fourth hand has permeated the art 
systems of even the elementary schools. Further study at first hand 
is to be recommended. The son, Mr. A. E. O. Munsell, devoted 
much time and considerable treasure in further amplifying the color 
system and secured the assistance of a distinguished group of scien- 
tifically trained people in making exact studies of colors. Among 
other results a series of colored papers were prepared which con- 
formed as nearly as possible with the theoretical requirements of the 
color system and illustrate equal spacing of hue, lightness, and 
saturation of colors as determined by the direct observation of several 
trained individuals. 

These papers, of remarkable uniformity and permanence, are made 
commercially available by the Munsell Color Company, Baltimore. 19 
A series of charts in which are collected these color samples is called 
the Munsell "Book of Color." 

A typical series of samples or color chips sent to the Massachusetts 
Institute of Technology has received spectrophotometric analysis by 
Glenn and Killian 20 on the Hardy automatic spectrophotometer, and 
complete color analysis in accordance with the ICI method is avail- 
able to interested persons. It is hoped that before long the results 
will be published. Owing to the meticulous care in the original paint- 
ing of the color samples to secure accuracy, uniformity, and perma- 
nence, their subsequent storage and painstaking methods of distribu- 
tion, coupled with the measurements made upon typical samples, 
they have proved to be the best stepping stones for the preparation 
and preservation of other color standards. 

Further studies of color and even of a possible re-spacing of the 
Munsell colors is now in progress, sponsored by the Colorimetry 
Committee of the Optical Society of America. All the members of the 
Subcommittee working on this problem are active delegates of the 
Inter-Society Color Council. 

Another atlas, the Maertz and Paul Dictionary of Color, having 
printed charts in many colors, is available. One main purpose in pre- 
paring this atlas was to illustrate as many as possible of the vast 
array of color names that have accumulated through the ages. Many 
of the color samples have been analyzed as far as possible and are now 
expressed in terms of the Munsell system and can, therefore, be ex- 
pressed in terms of the ICI chart. - 

The U. S. Pharmacopoeia and the National Formulary, American 
Pharmaceutical Association, which are part of the necessary equip- 



Oct., 1940] COLOR THEORIES 377 

ment of every drugstore in the country, describe the color of the 
drugs and chemicals. The names used in these descriptions have 
accumulated from many sources at various times, and with no official 
standard names the editors were appalled with the jumbled inexacti- 
tude of the resulting descriptions. An appeal first made to the 
Bureau of Standards led to the formation of the Inter-Society Color 
Council. 

FORMATION OF THE INTER-SOCIETY COLOR COUNCIL 

The Inter-Society Color Council grew out of a color conference 
and exhibit sponsored by the Revision Committee of the U. S. 
Pharmacopoeia at Washington, May 14, 1930, Professor E. N. 
Gathercoal in charge. Several proposals were considered for further- 
ing this work, such as the formation of a new color society, referring 
the whole matter to the Colorimetry Committee of the Optical So- 
ciety of America, or asking the National Bureau of Standards to do 
the work. The initial form in which the Council was set up resulted 
from a proposal of the late Mr. Irwin G. Priest, at that time the 
leading figure in the progress of color. This proposal in the form of a 
resolution which had been discussed and adopted by the Executive 
Committee of the Optical Society of America read: 21 

It is the sense of the Executive Council of the Optical Society of America that 
the need for better organization of those interested in the description and specifica- 
tion of color which found expression at the "Color Conference" held in Washing- 
ton, May 14, 1930, can best be met by the formation of a joint council consisting 
of officially designated representatives of the several national societies and associa- 
tions interested in the description and specification of color. 

The Inter-Society Color Council was formed essentially as pro- 
posed by Mr. Priest. Its articles of organization and procedure can 
be briefly paraphrased. The aims are to stimulate and coordinate 
the work of the various member societies so far as they relate to 
color. There are at present two types of memberships, (a) member 
bodies, (b) individual members. 

(a) Member bodies must be societies of national scope, operating 
on a non-profit basis. The ultimate authority for policies and 
affairs of the council is vested in the member bodies. Member bodies 
pay $25 yearly dues and are entitled to appoint at least three but not 
more than ten accredited delegates who represent that member body 
in all the activities of the council. (The Society of Motion Picture 



378 H. P. GAGE [j. s. M. P. E. 

Engineers has at present three delegates and is thus entitled to appoint 
seven more.) 

Three of these delegates shall be designated by the member body 
which they represent as voting delegates, one of which shall be desig- 
nated by the member body as the chairman of the delegation. The 
duty of this chairman is to report to the member body all proceedings 
of the Council of interest to the member body and to transmit to the 
proper officials of the member body any reports of the council that 
he thinks should appear in the publications of the member body. It 
is also one of the duties of the accredited delegates in general and the 
chairman of each delegation in particular to bring to the Inter-Society 
Color Council any problems of particular interest of his member body 
in the field of color. 

(b) Individual members, dues $5 per year, have all privileges of 
accredited delegates except that they may not hold office. The indi- 
vidual delegates as a group may elect three of their members who be- 
come accredited delegates with the privilege of voting and holding 
office. All members and voting delegates receive copies of the News 
Letter, minutes of the meetings, and reprints of technical papers pre- 
sented at joint sessions of the council held with member bodies. The 
total income of the council amounts to about $600 per year. 

The Council at present is made up of 74 delegates appointed by 11 
member societies, and by 67 individual members. It functions as a 
joint committee on color of the member societies favored with the 
advice of the individual members. 

Each delegation functions much as does any technical committee 
of a society. It is supposed (1) to secure papers of interest to the 
Society, to be presented at conventions and published; (2) to secure 
agreement on technical matters involving many individuals or har- 
monize diverse interests, particularly when such interests are repre- 
sented also in other societies; (3) to standardize; (4) to collect 
authoritative information; or (5) to encourage research. 

All these functions can often be more effectively performed when 
meeting with delegates and experts representing other organizations 
but interested in the same common object. Reading the list of mem- 
ber bodies should make the possibilities evident. These are : 

American Association of Textile Chemists and Colorists 
American Ceramic Society 
American Psychological Association 
American Society for Testing Materials 



Oct., 1940] COLOR THEORIES 379 

Illuminating Engineering Society 

National Formulary, American Pharmaceutical Association 

Optical Society of America 

Technical Association of the Pulp and Paper Industry 

The Textile Color Card Association of the United States 

U. S. Pharmacopoeial Convention 

The Society of Motion Picture Engineers 

In developing the color names recommended to the U. S. Pharma- 
copoeial Revision Committee, 22 the Council obtained for one of its 
member bodies the advice of the color experts of two other member 
bodies (the Optical Society of America and the American Psychologi- 
cal Association) ; it obtained for this member body the cooperation 
of the National Bureau of Standards, which had previously been 
sought and refused; and the Council served as an authoritative source 
of information not swayed by commercial considerations for deciding 
which of the various competing systems of material color standards 
was best suited to derivation of the color names. In all this work 
the allied interests of another member body (the Textile Color Card 
Association) were protected by the presence of its delegates at the 
Council meetings. 

It may not be amiss at the present time to mention specifically the 
work of another of the member bodies. In the clothing, house furnish- 
ing, and other industries catering to the retail trade, many fancy color 
names are used with the idea of attracting the attention of the style- 
conscious public. As examples of such fancy names the following 
may be quoted from recent advertisements occurring in the New York 
newspapers: 

Sleeping Blue Dusty Rose Trichlor 

Daring Pink Daring Red Maize 

Matisse Blue Solar Yellow Heaven Pink 

Blossom Blue 

To the scientific-minded such names are hardly informative, but 
to the cool-headed business men who are responsible for furnishing 
these colors in many types of clothing, and who wish to combine other 
articles of apparel from hats, blouses, sweaters, skirts, stockings, 
shoes, rubbers, purses, buttons, to curtains, tapestry furniture covers, 
and any other things that must either be alike or must harmonize, 
such names should be as fully standardized as anything else, or the 
manufacturers of dyestuffs, the weavers, the dyers, the manufacturers 
of rubber, leather, and miscellaneous fixings would be in such utter 



380 H. P. GAGE [J. S. M. p. E. 

confusion that economic manufacture of the gaily colored and 
rapidly changing styles would be utterly impossible and the smooth 
assembling of harmonious color combinations would be in the state 
of utter confusion of a century ago. 

In order to remedy this situation the Textile Color Card Associa- 
tion of the United States, Inc., was established in 1915 for the pur- 
pose of standardizing commercial colors for the benefit of industry 
to give accurate information to the manufacturers of such articles. 

Upon inquiry of Mrs. Rorke, Secretary of the Textile Color Card 
Association, it was found that the above fancy color names are to the 
manufacturers not as vague as they would appear to the public. 
Each is the result of carefully prepared samples which have been dis- 
tributed to the manufacturers and can at present be represented 
fairly accurately in the Munsell system. It is expected that the next 
revision of the Standard Color Card of America, which is the 9th 
edition, containing about two hundred colors, will not only bear the 
fancy names but they will be defined in exact spectrophotometric mea- 
surements and expressed in terms of the chromaticity diagram of the 
ICI 1931 Standard Observer and coordinate system, and also in terms 
of the Munsell Book of Color, the Maertz & Paul Dictionary of Color, 
and the ISCC NBS (Inter-Society Color Council National Bureau 
of Standards), standard color names. 

As previously mentioned, the particular irritation that started 
the formation of the Inter-Society Color Council was the search for 
a good set of color names. This was not difficult, but it was a much 
more laborious task to ascertain which colors best fitted these names ; 
that is, what colors most people would associate with these names. 
This work is best described 23 in Research Paper RP1239 of the Bureau 
of Standards, "Method of Designating Colors," by Deane B. Judd 
and Kenneth L. Kelly. As usual with government Bureaus, the re- 
sults are as impersonal as possible but it was practically a necessity 
to express the results in terms of the sample "chips" in the Munsell 
Book of Color. Not only were these color chips used but also special 
colored papers, carefully measured on the spectrophotometer, were 
made available for the investigation by the Munsell Color Company. 
The problem was presented to the Color Council in the following 
words : 

A means of designating colors in the U. S. Pharmacopoeia, in the National 
Formulary, and in general pharmaceutical literature is desired ; such designation 
is to be sufficiently standardized as to be acceptable to science, sufficiently broad 



Oct., 1940] COLOR THEORIES 381 

to be appreciated by art and industry, and sufficiently commonplace to be under- 
stood, at least in a general way, by the whole public. 

Briefly described, the hues of all colors will be designated by five 
well known color names, red, orange, yellow, green, and blue, typical 
of the spectrum and four others, purple, pink, brown, and olive. 
At first it was attempted to designate certain browns as dark orange, 
as indeed they are, but later it seemed more advantageous to keep 
the more usual names. Similarly, pink and olive are so well known 
as to make other names seem artificial. The result is that some hues 
have two or three names, depending upon whether a light or dark 
representative is described. This description can best be illustrated 
in Table I. The use of abbreviations is encouraged. When a hue is 
about halfway between two main hues, both names are used and 
both initials are capitalized. When one hue is used only as a modi- 
fier to indicate the direction in which the color is altered, the suffix 
ish or a lower-case initial is used. 

TABLE I 

Table of Hue Designations 

Red or pink R or Pk 

Reddish orange, or orange pink, or reddish brown r O O-Pk r Br 

Orange or brown O, Br 

Yellowish orange or yellowish brown Y O, Y Br 

Yellow or olive brown Y Ol-Br 

Greenish yellow or olive gY Ol 

Yellow green or olive green YG Ol-G 

Yellowish green yG 

Green G 

Bluish green b G 

Greenish blue g B 

Blue B 

Purplish blue p B 

Bluish purple b P 

Purple P 

Reddish purple r P 

Red purple or purplish pink R P or p Pk 

Purplish red or pink p R or Pk 

The relative reflecting power or lightness of the colors is designated 
by the five terms very dark, dark, medium, light, very light, making five 
rough gradations in this respect. 

The saturation or vividness of the colors have six designated de- 
grees, but the names differ in accordance with the lightness of the 



382 



H. P. GAGE 



[J. S. M. P. E. 



color approximately in accordance with the following design: (1) 
neutral: white, gray, or black; (2) nearly neutral, but inclined 
toward one of the named hues : use the suffix ish, as reddish, pinkish, 
brownish, yellowish, olive, greenish, bluish, purplish (Table II). 







TABLE II 








White 


-ish white 


Very pale 


Very light 






Light gray 


Light-ish gray 


Pale 


Light 


Brilliant 


Vivid 


Medium gray 


Medium-ish gray 


Weak 


Moderate 


Strong 


Vivid 


Dark gray 


Dark-ish gray 


Dusky 


Dark 


Deep 


Vivid 



Black 



-ish black 



Very dusky Very dark Very deep 



With this system of names in mind it was necessary to designate 
the exact color to which each name should apply, and to set the limits 
between which each name should be used. This work was done 
mostly with colored samples supplied by the late Walter T. Spry of 
the Munsell Color Company. Part of these were the regular series 
used in the Munsell Book of Color and part of them were special. All 
the significant special samples have been measured for their colors. 

A second proposal of the Committee on Color Problems 24 is a code 
in which to express approximately the spectral transmission of color- 
filters or the spectral reflectance of colored objects. 

Certain standard wavelengths are used for the measurements. 
The transmission for each wavelength is expressed in numbers from 
to 9, assigning certain values for each numeral. The entire spec- 
tral curve is expressed in a number of seven digits, as 5100999 for a 
rose pink, or 8710004 for a medium blue. 

The wavelengths used and the transmissions to be expressed by 
each numeral are as given in Table III. 



Digit 

1st 
2nd 
3rd 
4th 
5th 
6th 
7th 



Wavelength 

Millimicrons 

440 
480 
520 
560 
600 
640 
680 



TABLE HI 

Digit 


1 
2 
3 

4 
5 
6 
7 
8 
9 



less than 0.01 
0.01 to 0.04 
0.04 to 0.08 
0.08 to 0.15 
0.15 to 0.25 
0.25 to 0.35 
0.35 to 0.45 
0.45 to 0.60 
0.60 to 0.75 
more than 0.75 



Oct., 1940] COLOR THEORIES 383 

In addition to the two major projects just described, the Council 
has prepared a survey of the standard color terms used by the 
different member bodies. The first draft is a 42-page mimeograph 
pamphlet. 

A list of persons outstanding in scientific, technical, educational, 
and industrial fields of color, but not including all users thereof, has 
been collected and printed under the title of Who's Who in Color, 
which can be obtained through the secretary of the Council.* Avail- 
able also are large coordinate sheets of the ICI mixture diagram, and 
the symposium on color tolerance; copies of the 1938 symposium 
on the Hardy recording spectrophotometer included in the October 
1938 Journal of the Optical Society of America; of the 1940 sym- 
posium on spectrophotometry in the Paper Industry; and other 
symposiums on the subject of color will be obtainable as they become 
available. 

The Inter-Society Color Council is what its name implies, a joint 
committee formed from several societies. Its News Letters issued to 
its members in mimeograph form to describe the progress of color 
work, notices of important color publications, the activities of its 
planned meetings, is not intended as a competing journal, but, with 
the minutes of the meetings, serves as a basis for reports by the dele- 
gates to the member societies which can be printed in their own publi- 
cations. 

The Council sponsors meetings with the member societies on the 
subject of color. The resulting papers have appeared in the journals 
of the respective societies, and in reprints distributed to the delegates 
and members. Such joint meetings have been held with the Optical 
Society of America, The Technical Association of the Pulp and 
Paper Industry, and The American Psychological Association. A 
joint technical session has been scheduled during the convention of 
the Illuminating Engineering Society, September 9th-12th at Spring 
Lake, N. J., and another during the 1941 spring meeting of the 
American Society for Testing Materials, to be held at Washington, 
D. C., in March, 1941. It is hoped that a similar joint meeting may 
be arranged some time in the future with the Society of Motion 
Picture Engineers. 



* Miss Dorothy Nickerson, c/o Agricultural Marketing Service, Washington, 
D. C. 



384 H. P. GAGE [j. s. M. p. E. 

REFERENCES 

1 HECHT, S. : "The Development of Thomas Young's Theory of Color Vision," 
/. Opt. Soc. Amer., 20 (May, 1930), p. 231. 

2 Report of the Committee on Colorimetry, J. Opt. Soc. Amer., 6 (1922), p. 
527. 

3 "Frederick Eugene Ives" An obituary, J. Soc. Mot. Pict. Eng., XXIX 
(Aug., 1937), p. 219. 

4 IVES, H. E.: "Telephone Picture Transmission," /. Soc. Mot. Pict. Eng., 
XXIII (Oct., 1925), p. 82. 

5 GIBSON, K. S. : "The Analysis and Specification of Color," /. Soc. Mot. Pict. 
Eng., XXVIII (Apr., 1937), p. 388. 

6 JUDD, D. B.: "Color Blindness and Anomalies of Vision," J. Soc. Mot. Pict. 
Eng., XXVI (June, 1936), p. 616. 

7 WILLIFORD, E. A.: "Citation on the Work of Dean Brewster Judd," /. Soc. 
Mot. Pict. Eng., XXIX (Dec., 1937), p. 580. . 

8 GOLDEN, N. D.: "Citation on the Work of Kasson Stanford Gibson," J. 
Soc. Mot. Pict. Eng., XXXI (Dec., 1938), p. 553. 

9 MACADAM, D. L.: "Physics in Color Photography," /. Applied Physics, 
XI (Jan., 1940), p. 46. 

10 MACADAM, D. L.: "Subtractive Color Mixture and Color Reproduction," 
J. Opt. Soc. Amer., XXVIII (1938), p. 446. 

11 YULE, J. A. C.: "Theory of Subtractive Color Photography," /. Opt. Soc. 
Amer., XXVIII (1938), pp. 419, 481. 

12 MEES, C. E. K. : "An Atlas of Absorption Spectra," Longmans, Green and 
Company, 1909. 

13 "Wratten Light Filters," Eastman Kodak Co., 15th Ed., 1938. 

14 Commission Internationale de 1'Eclairage: "Compts Rendu des Seances, 
Cambridge," (Sept., 1931), pp. 19-29, 647-655. 

16 SMITH, T., AND GUILD, J. : "The I.C.I. Colorimetric Standards and Their 
Use," Trans. Opt. Soc. (England), XXXIII (1932), pp. 73-131. 

16 JUDD, D. B. : "The 1931 1. C. I. Standard Observer and Coordinate System 
for Colorimetry," J. Opt. Soc. Amer:, XXIII (1933), pp. 359-374. 

17 GIBSON, K. S., AND WALKER, G. K.: Signal Section Proceedings, American 
Railway Association, XXX, pp. 380-443; XXXV, pp. 122-143; XXXVI, pp. 136- 
162. 

18 HARDY, A. C.: "Handbook of Colorimetry," The Technology Press, Massa- 
chusetts Institute of Technology, Cambridge, Mass.. 1936. 

19 "Munsell Book of Color," Munsell Color Company, Inc., Baltimore, Md., 
1939. 

20 To be published in J. Opt. Soc. Amer. 

21 J. Opt. Soc. Amer., XXVIII (Oct., 1938), p. 357. 

22 JUDD, D. B.: Bull. American Ceramic Society, XIX (Sept., 1938), p. 379. 

23 JUDD, D. B., AND KELLY, K. L.: "Method of Designating Colors," /. Re- 
search of National Bureau of Standards, XXIII (Sept., 1939), RP1239. 

24 JUDD, D. B.: "Designation of Filters for Theatrical Lighting," J. Opt. Soc. 
Amer., XXVIII (1938), pp. 390-397. 



Oct., 1940] COLOR THEORIES 385 

26 PRIEST, I. G.: "Apparatus for the Determination of Color in Terms of 
Dominant Wavelength, Purity, and Brightness," /. Opt. Soc. Amer., 8, pp. 28 
and 173. 

DISCUSSION 

DR. GOLDSMITH: Why are not simple numerical values suggested for the des- 
ignation of colors? Would it not be simpler to use numerical coefficients for 
color designation rather than such vague terms as turquoise, lilac, or pink, for 
example? If a standard color-temperatur were selected for the illumination, 
and the trichromatic components of a color determined on a standard equipment 
having fully disclosed characteristics, the color designation would be definite. 
Should there not also be provided a relatively simple piece of apparatus capable 
of duplicating such designated colors speedily for the use of those who have an in- 
terest in definite color values? And is it not further a fact that in the long run 
verbal designations will hardly prove as adequate as numerical designations? 

DR. GAGE: That was carefully studied, but we would get a designation in x 
and y which was very accurate. The Railway and Aviation specifications say 
the y of a certain red glass, for example, shall not exceed 0.295. It is all right for 
specification purposes, but the ordinary individual would not understand it. 

DR. GOLDSMITH: The type of color -producing equipment which seems to be 
needed would be one having, for example, three adjusting dials on it which might 
be set to the trichromatic coefficient values of a particular color. That color might 
then appear on a screen or sheet of ground-glass or similar surface. If such a 
device were capable of practical production at this stage of the art it would ap- 
pear to be the most convenient and readily usable solution to the color-matching 
problem. 

DR. GAGE: I am going to answer that quite frankly and tell you what the 
people working on that kind of thing have actually found. An elaborate ap- 
paratus was assembled at the National Bureau of Standards 26 in which a single 
wavelength of the spectrum could be mixed with white light and compared 
directly with the color being studied, after which the per cent white and spec- 
tral color was measured. This method has not been continued as it did not prove 
to be as satisfactory as finding the position of a color on the chart from its 
spectrophotometric measurements. These curves can now be easily made with 
the Hardy spectrophotometer and analyzed in such a way that we get the x and 
y coordinates of the color and its reflection factor. That is the accurate way of 
doing it. It is not the way that we can honestly recommend for ordinary color 
work with the hope of being understood by the average individual. The inter- 
pretation of results expressed in the x and y coordinates can be done in this way: 
The standard color papers in the Munsell Book of Color have all been studied by 
Glenn and Killian, working at the Massachusetts Institute of Technology under 
Professor Hardy. Standard samples have been measured on the spectropho- 
tometer. We know their x and y coordinates. Therefore, when we take a copy of 
this Munsell Book of Color, we can refer to that and say that a given sample 
has such x and y coordinates. Or, if we say that here is a color which has certain 
x and y coordinates, what does it look like? We can refer to the table and find 
out which of the samples in the chart will have those x and y coordinates. Much 
the same analysis is being done with the Maertz & Paul Dictionary of Color that 



386 H. P. GAGE tf. s. M. P. E. 

was gotten out for another purpose. That shows the color names for all these 
colors which have appeared through the ages turquoise blue and Nile green, and 
so on. 

DR. GOLDSMITH: In Maertz & Paul's Dictionary of Color there are about a 
thousand definitely named colors and perhaps four times as many unnamed 
colors. It takes a considerable amount of time to locate any specific color. It is 
by no means certain that, in color matching, the effect of the illumination to which 
the color samples are subjected for examination or comparison does not influence 
too greatly the matching results. It is also uncertain whether the degree of matte 
structure of the color sheets in the "dictionary" and in the color sample may not 
be sufficiently different to invalidate the matching results at certain angles of 
illumination. Can such color -matching methods serve as more than a first ap- 
proximation, as compared to the precision of trichromatic-coefficient determina- 
tion or spectrophotometric measurements? 

DR. GAGE: It is a first approximation and I would suspect that about 400 
years from now the Munsell papers would not have exactly the same color 
and would not have the same position on the triangle that they have now. It 
would be possible, at that time, to measure them on a spectrophotometer, and 
find out where they were on the triangle and tell how much they have drifted, to 
mix up some more colors and get back to the exact colors we have now. 

DR. GOLDSMITH: Do you believe that the printed sheets of colors are rea- 
sonably permanent? 

DR. GAGE: They are the best that can be had in material standards. They 
have not drifted enough so that anybody can tell yet that they have drifted. Of 
course, it is not known exactly what they were ten years ago. 

MR. CRABTREE: One of our immediate interests is the specification of paints 
and drapes used in the studios for color photography. How do you designate 
them at the present time? 

MR. HOB ART: In the color-control department the charts are used for the 
general purpose of letting the people in the studio see what range of colors is 
available. Colors for costumes or sets are chosen chiefly from past experience. 
The producer is shown a sample of the color and the result on the screen after 
the color is photographed in Technicolor. 

MR. KELLOGG : There is a special consideration in judging colors of liquids as 
would be required for druggists. It would seem that samples of opaque colors on 
a chart would be very different. When judging the color of a liquid, it is usually 
held up to a light, and one shade is seen when looking through a considerable 
thickness and another shade when looking through only a little of the liquid. 
Would a wedge on a card or a wedge of stained glass be any better for comparing, 
or as a visual standard, than a simple solid block? 

DR. GAGE : The method which was worked out and which was reported in the 
Bureau of Standards research paper on the subject, is to put the liquid in a stand- 
ard cell, and hold it up so as to look through the liquid at a white paper illuminated 
with the same light as the Munsell pages. When you find the chip which comes 
nearest the color of the liquid in the cell under those conditions, that is the name 
that you give it. 

Of course, great precision is not required in this. There are only about 150 
color names in this system. The New York Times published a statement that 



Oct., 1940] COLOR THEORIES 387 

there were something like 2,000,000 different colors; actually, a good eye can per- 
ceive something like 10,000,000 colors. If precision is required, a spectrophoto- 
metric curve is made. 

A piece of yellow paper might actually have no yellow in it whatever; only red 
and green, with the yellow taken out. Or it might have yellow and nothing but 
yellow. But one may wish to know which type of yellow it is, which might be 
of importance in photography. Two colors may look alike to the eye but would 
photograph differently. 

All those things can be determined by careful analysis; but if only a general 
idea of whether a liquid is a saturated color, for example, or a weak color, or 
whether it is, in general, red, green, or blue, light or dark, the system of color 
names is adequate. 

MR. MARTIN: I spent a number of years in an experimental theater where 
we used the Munsell Color System for keeping a record of the colors used in 
settings and properties, and found it valuable when it was necessary to reproduce 
them at future presentations of the same show. This application of the Munsell 
Color System is still being used at the same theater, more as a record of what has 
been done than in planning original sets. 

MR. CRABTREE : Did you run into any snags, or was it adequate? 

MR. MARTIN: We found it adequate in describing the colors. The difficulty 
was in matching them the second or third time. But we usually came close. 

MR. RICHARDSON: In the beginning color on the screen was very poor, be- 
cause only a few of the finer shades could be reproduced. Have any tests been 
made to show how far we have advanced in the rendition of color on the theater 
screen? 

DR. GAGE: Some work on that was done by MacAdam, Yule, 9 ' 10 ' 11 and 
others, and was reported in the Journal of the Optical Society of America. They 
made a very thorough analysis of how much distortion is likely to occur in the 
subtractive process, and of methods of correcting it by special additional print- 
ings. A given process is likely to produce distortion in a certain way. Instead of 
projecting distorted colors on the screen, or colors we do not want, why not dis- 
tort the colors in front of the camera, so that when they appear on the screen they 
will be correct? 

All such things are receiving most excellent study. 



THE THEATER STANDARDIZATION ACTIVITIES 
OF THE 

RESEARCH COUNCIL OF THE 
ACADEMY OF MOTION PICTURE ARTS AND SCIENCES* 

JOHN K. BILLIARD** 



The Research Council of the Academy of Motion Picture Arts and 
Sciences, handling cooperative technical problems for the industry, 
is, by its very nature, interested in many of the problems confronting 
theater owners. 

The Research Council was organized in 1934 by the major Holly- 
wood studios for the fundamental purpose of getting pictures of better 
quality upon the screen at a lower net cost through higher net 
efficiency. 

After its organization, the Research Council devoted most of its 
time to problems concerned primarily with motion picture produc- 
tion especially the coordination of sound recording within the 
various studios. 

Preliminary Work. When investigating that subject, we found 
that the sound reproduction in different theaters varied to such an 
extent that it was impossible to obtain uniform quality under existing 
conditions. It was very evident that a coordinating program was 
vitally necessary. As a result the Research Council Theater Stand- 
ardization Committee was appointed late in 1936. 

As a first step in this program, the Committee conducted hundreds 
of listening tests in many different theaters, in order that each mem- 
ber of the Committee would have a wide experience with field con- 
ditions and so that all members of the Committee would have a 
common understanding upon which to base this program. 

Each member of the Committee is a technical expert in the field 
of sound and all the past experience of the Committee, coupled with 

* Presented to the Pacific Coast Conference of Independent Theater Owners 
at Los Angeles, May 9, 1940. 

** Chairman, Research Council, Theater Sound Standardization Committee. 

388 



THEATER STANDARDIZATION ACTIVITIES 389 

this group experience, has given us a wide knowledge and under- 
standing of the subject which has proved to be of tremendous benefit 
to us in our Committee work. 

Early in this program we assembled a test-reel containing a short 
length of a regular release print from each of the studios. This 
assembled reel, with both picture and sound, was used as a means of 
coordinating listening tests held in the theaters. 

This particular test-reel proved to be so valuable to us here in 
Hollywood, that prints were made available at cost, upon request, 
to service companies, equipment manufacturers, and theaters. Since 
its original release we have revised and shortened the reel and the 
several hundred prints now in use throughout the world have been 
of great help in adjusting theater equipment. 

All the major theater service and manufacturing companies are now 
using the Research Council Theater Sound Test Reel to adjust theater 
equipment on a uniform quality basis. 

As you will realize, our ultimate aim is to make sound from all 
studios reproduce equally well in each theater at least to bring all 
theaters up to a commercially acceptable quality-level. 

The Research Council naturally recognizes the value of engineering, 
testing, and checking of theater equipment, but we have based our 
entire theater standardization program upon the fundamental fact 
that the final determination should be a listening test, and I mean 
a listening test of the equipment as installed and adjusted in the 
theater. For this reason all our standards have been based so far 
upon listening tests correlated with engineering data. 

From an engineering standpoint, the ultimate aim in this work is 
the specification of acoustical standards which will place these listen- 
ing tests upon a scientific basis. At the present time there is not 
sufficient acoustical information available upon which to base any 
standard acoustical specifications. The Research Council has a 
Committee working on this problem, which we hope will eventually 
assemble enough data to permit setting up standard methods of 
acoustical measurements that will be of use in adjusting theater 
equipment. 

STANDARD METHODS FOR THEATER ADJUSTMENT 

As a result of the Committee's experience and listening tests with 
our theater reel, a standard method of theater adjustment for all the 
better known sound systems has been set up and, wherever possible, 



390 J. K. HlLLIARD [J. S. M. P. E. 

equipment manufacturers and service organizations are following 
these specifications when installing and maintaining equipment. 

Experience has shown that the use of these standard adjustments 
leads to the best overall quality obtainable with current sound record- 
ings as reproduced on theater equipment with two-way horn systems. 
In most cases a slightly different adjustment is necessary for each 
make and type of loud speaker system. However, hundreds of recent 
installations have borne out the fact that if theaters are so adjusted, 
the product of any one producer is not penalized, and the overall 
quality of all product is more uniform. 

The quality obtained is modified, of course, by acoustical conditions 
in the theater itself, but it has also been found that even where bad 
acoustical conditions exist the effect of these conditions on the product 
is minimized if these standard adjustments are used. 

The usual manner in which this type of standardization takes place 
is through the manufacturing and service organizations, as they are 
in closer touch with the studios and with technical advancements 
which may take place at the source of the product. Accordingly, the 
exhibitor is not always conscious of the fact that this sort of progress 
is taking place. Consequently we are striving to make our activities 
of actual, tangible benefit to the exhibitor. 

PERFORMANCE STANDARDS FOR THEATER SOUND EQUIPMENT 

One thing which we have done along this line is to prepare recom- 
mendations on performance standards for theater sound-reproducing 
equipment. Prior to the issuance of these recommendations, you as 
exhibitors were forced to rely primarily upon statements of salesmen 
for information as to equipment which you might be considering for 
purchase. 

After conferences extending over a year's time, participated in by 
representatives of the studio sound departments, equipment manu- 
facturers, and the theater servicing groups, the Research Council 
published these recommendations, and you as exhibitors now have 
an unbiased, impartial source of information on the standards up 
to which any sound equipment should measure. 

While we do not, of course, advise on specific equipments by name, 
we have set up minimum requirements for equipment performance 
which are sufficient to guide you in these matters. One thing you 
may be sure of if you follow our recommendations, you will avoid 
buying equipment which is not representative of the best available. 



Oct., 1940] THEATER STANDARDIZATION ACTIVITIES 391 

On the other hand, such equipment will have no unnecessary features 
which would add to the cost of installation and maintenance. 

Our standardization activities have been considered so important 
by the sound equipment manufacturers that during the past few 
years all the major equipment manufacturers have sent representa- 
tives to Hollywood to consult with us every few months. In addi- 
tion, permanent Hollywood representatives are maintained here by a 
number of companies who cooperate with the Committee and with 
whom we are in constant consultation. 

Thus, you can be assured that the Hollywood studios and the 
sound equipment manufacturers are going along step by step, and 
this cooperation between these two groups of the industry will insure 
your getting the maximum benefit from every dollar spent by you on 
equipment replacement or maintenance. 

The Committee has spent many hours in conference with repre- 
sentatives of these manufacturers, discussing the design of individual 
equipments so that new equipments brought out from time to time 
will give the best possible quality with current studio recordings. 

As a result of this phase of our program it is now possible for the 
exhibitor to purchase better sound equipment at a lower price than 
would have been possible without the Committee's coordinating 
efforts. While the Committee can not, of course, claim credit en- 
tirely, we believe, for example, that we have contributed to making 
it possible for you now to purchase 50 watts of power in your equip- 
ment for the approximate price of 2 1 /* watts ten years ago. 

POWER REQUIREMENTS FOR THEATERS 

Let me briefly discuss the matter of power. Many people believe 
that the volume of sound that is, the loudness that can be obtained 
in a theater depends entirely upon the amount of power installed. 
This is only partially true. Power is required for increased loudness 
for the proper presentation of special effects such as the earthquake 
in San Francisco, the breaking up of the icebergs in Spawn of the 
North or the breaking of the dam and the resulting flood in The Rains 
Came. But also from a quality standpoint adequate power is neces- 
sary to reproduce dialog and music at normal levels without harsh- 
ness and unnaturalness. 

As a result of a great deal of study of amplifier power requirements, 
the Academy Research Council is issuing recommendations on the 
minimum power requirements for theater sound systems. These 



392 



J. K. MILLIARD 



[J. S. M. p. E. 



recommendations indicate the minimum power which should be in- 
stalled in any theater in order to give proper reproduction of current 
sound recording. Fig. 1 indicates these minimum power require- 
ments. 

You will note that the following power for specific seating capaci- 
ties is required : 



Number of Seats 

0- 400 
400- 600 
601- 750 
751-1000 
1001-1250 
1251-1500 
1501-1750 
1751-2000 
2001-2250 
2251-2500 
2501-2750 
2751-3000 
3001-3250 
3251-3500 
3501-3750 
3751-4000 
4001-4250 
4251^500 
4501-4750 
4751-5000 
5001-5250 
5251-5500 
5501-5750 
5751-6000 



Minimum Power 
Requirements 

10 watts 

13 

15 

20 

26 

32 

37 

43 

48 

53 

59 

65 

70 

76 

82 

88 

93 

98 
104 
110 
115 
121 
126 
132 



It can be easily recognized that the minimum power of 10 watts is 
entirely within reason. The average modern radio in your home has 
5 watts, and the better sets have 10 to 15 watts of power. You may 
rest assured that this amount of power would not be available unless 
it was necessary from a quality standpoint especially in this day of 
inexpensive radios where price competition is so important. 

We hope that the exhibitors will take advantage of our work and 
will consult our recommendations when you purchase any equipment 
so you will receive at least the power recommended for whatever size 
theater you are equipping. 



Oct., 1940] 



THEATER STANDARDIZATION ACTIVITIES 



393 



All of Hollywood's sound is being recorded with these power re- 
quirements as a basis, and if these recommendations are followed you 
will be assured of obtaining the best possible quality from all types 
of recording. 

Adequate power as recommended by the Research Council is of 
definite commercial value to you, as it gives you sound quality com- 
parable to the best available and increases customer enjoyment. 




FIG . 1 . Academy Research Council minimum power requirements for theaters 
(minimum recommended amplifier output based upon seating capacity of 
the auditorium). 

THEATER ACOUSTICS AND SOUND LOUDNESS IN THE AUDITORIUM 

I might point out one fact which has become very apparent to us 
since the start of our work that many theaters encounter difficulties 
with their sound because of acoustic deficiencies. Our experience 
indicates that many exhibitors do not realize the necessity of attempt- 
ing to remedy these acoustic deficiencies rather than to try to get 
around them by means of electrical adjustment of the sound equip- 
ment. 



394 J. K. MILLIARD [j. s. M. P. E. 

Often only a few dollars worth of material properly placed in the 
auditorium or backstage will improve results tremendously by 
giving greater sound uniformity throughout the theater so that the 
maximum number of seats, regardless of their position in the audi- 
torium, can be utilized with no discomfort to the audience. 

Theater owners often spend considerable money and give lots of 
thought to the subject of comfort. You work diligently to achieve 
eye comfort by putting a good picture on the screen. You spend 
money for good seats and carpets. You maintain clean and well 
equipped rest rooms, and attractive lobbies. But one type of com- 
fort which in our experience we have found to be neglected is ear 
comfort. If your patrons must strain to hear the sound, or if they 
are subject to raucous and overlouded sound, they will become tired 
just as rapidly from ear fatigue as from eye fatigue or bodily dis- 
comfort. 

To achieve ear comfort, it may not be necessary to spend lots of 
money. Poor sound conditions can be corrected very often at small 
cost, the main effort being proper technical information and the 
manner of applying it. 

Difficulty encountered in setting volume level in many theaters 
also results from acoustic deficiencies, in particular because of non- 
uniform distribution of sound throughout the house. This problem 
is decreased or entirely eliminated with proper distribution through- 
out the auditorium as given by recommended two-way speaker sys- 
tems, which are universally considered to give the best results of any 
speakers now available. 

We have received complaints from time to time from the field 
stating that some release prints will not run throughout the show on 
one fader setting. We realize that all of you are concerned with this 
problem. In the majority of cases this trouble can be traced either 
to poor acoustical conditions or to improper sound equipment adjust- 
ments. Where an auditorium is highly reverberant in particular 
frequency bands for instance, where deep male voices are accen- 
tuated, the sound level in such sequences in the reel will appear too 
loud for other portions of the picture. This will necessitate a fader 
change in such a house, while in a theater with proper acoustics the 
same feature will play throughout on one fader step. 

Thus it may be seen that proper acoustics contribute tremendously 
to the ease and time, such as projectionist and servicemen's time, 
required to obtain the best sound quality and the proper volume, and 



Oct., 1940] THEATER STANDARDIZATION ACTIVITIES 395 

tend to maintain the proper sound level at a single fader setting 
throughout the feature. 

Here again the commercial aspect should be given consideration as 
poor acoustics lead to complaints at the box-office because of poor 
quality and improper sound level. 

VOLTAGE REGULATION 

A common difficulty leading to fader changes within a single feature 
is poor regulation of the power supply to the theater, i. e., the in- 
coming a-c line voltage from the power company's supply line varies 
from time to time. In many instances the change in line voltage is 
sufficient to vary the acoustic power in the auditorium as much as 
400 per cent. It is advisable in all installations where perfect line 
voltage regulation is not available to install a voltage regulator as 
part of the sound equipment. This voltage regulator will maintain 
a constant voltage to the equipment and thus a constant power level 
in the theater regardless of wide line voltage variations. 

INCREASING UNIFORMITY OF PRODUCT 

In the early days of sound, each producer made his product to 
conform to his own individual standards, thus necessitating constant 
adjustment by the serviceman as the theater ran the product of dif- 
ferent studios. At the present time you will find a much greater 
degree of uniformity of product than four or five years ago, and we 
are all continually striving to remove any differences still existing and 
to eliminate the necessity for any adjustment of theater equipment 
to fit individual product. 

The Academy Research Council is performing a real service to 
exhibitors at the present time by furnishing information to you, by 
setting standards for performance for theater equipment, and in 
helping to coordinate recording in the studios with reproduction in 
the theaters. Everyone connected with the organization is extremely 
proud of what has been accomplished since the start of this work. 

RESEARCH COUNCIL SERVICES TO EXHIBITORS 

We will be able to be of even greater service to you in the future by 
placing the facilities of the Research Council at your individual service 
to advise you on your equipment problems. Any exhibitor consider- 
ing the purchase of new equipment will be interested in knowing that 
all our Bulletins on theater standardization, including the one con- 



396 J. K. MILLIARD 

taining our recommendations on performance standards for theater 
equipment, are available to you and we will be glad to furnish copies 
upon request. 

If you are interested in receiving copies of these Bulletins, write to 
the Research Council office and we will be glad to send this material 
to you and place your name on our mailing list so that copies of future 
material of interest to exhibitors will come to you as issued.* We 
want you to know that the Research Council and its Theater Stand- 
ardization Committee are interested in your problems, and that we 
welcome your inquiries and your requests for information, and we 
stand ready at all times to cooperate in any way possible to assist 
you to get better quality in your theater. 

* Requests for this information should be addressed to the Academy Research 
Council, 1217 Taft Building, Hollywood, Calif. 



IMPROVEMENTS IN MOTION PICTURE LABORATORY 

APPARATUS* 



C. E. IVES AND E. W. JENSEN** 



Summary. A machine for cleaning motion picture film by dry wiping has been 
equipped with a reservoir and distributing system so as to fit it for application of a 
cleaning liquid. In order to prevent dust from being carried into the roll when film is 
rewound, the wind up is enclosed in a box into which filtered air is pumped at a suf- 
ficient rate to maintain a forceful discharge stream at the point where the film enters. 
This stream dislodges dust particles. 

In order to have sufficient light on a meter in a darkroom the face of the meter is 
covered with a metal hood containing a suitable safelight. The meter is observed 
through a small aperture which permits very little light to escape into the room. Self- 
luminous finder buttons used as markers in a darkroom can be protected from dirt 
and corrosion by mounting them in an inverted glass ignition tube which is sealed at 
the open end with a thermoplastic. 

A developing machine roller is provided with frictional driving engagement with the 
shaft on which it is mounted by the use of spring-held shoes which bear against the 
shaft. 

Oscillation in a mechanical filter in the drive train of a continuous printer has been 
subdued by the use of Koroseal strips in place of springs and friction damping. 

The present article is the third in a series 1>2 in which some twenty- 
five items related to motion picture laboratory equipment and prac- 
tices have been discussed. The subjects treated in this paper are as 
follows : 

(1) Cleaning equipment for negatives 

(2) A dust-free windup 

(5) The illumination of meters in a darkroom 

(4) A method of mounting self-luminous buttons 

(5) A friction drive roller. 

(6) A mechanical filter for printer driving 

(1) CLEANING EQUIPMENT FOR NEGATIVES 

It is found necessary to clean motion picture negatives before 
making the first print and then periodically during the making of 

* Presented at the 1940 Spring Meeting at Atlantic City, N. J., received 
May 14, 1940. Communication No. 766 from the Kodak Research Laboratories. 
** Eastman Kodak Co., Rochester, N. Y. 

397 



398 C. E. IVES AND E. W. JENSEN [J. s. M. P. E. 

release prints to remove dust, oil specks, and other loose or adherent 
material which, although present in such small quantity as not to be 
very noticeable on visual inspection, is quite offensive in a projected 
print. This is frequently done by passing the film between the sur- 
faces of a folded piece of silk plush wetted with carbon tetrachloride or 
other oil solvent. The plush pad is held in the hand while the film is 
drawn through its folds slowly enough to permit evaporation of the 
liquid so that it is not carried into the winding roll. 




FIG. 1. Modified Neumade cleaning ma- 
chine (front). 

Hand operation of the rewind has the advantage of requiring 
constant attention and permitting stops when necessary to give 
additional care where required. This procedure has the usual short- 
comings of discontinuous hand work where a well controlled uniform 
treatment is required throughout a considerable length of film. 
The rate of application of the cleaning solvent varies above and below 
the optimum and stops must be made several times when cleaning a 
1000-ft roll to apply more cleaning liquid. If atmospheric conditions 
are not favorable, moisture sometimes condenses on the surface of the 
pad when it is opened out for the addition of cleaning solvent and is 



Oct., 1940] 



LABORATORY APPARATUS 



399 



transferred to the film, causing spots. The plush is not utilized 
effectively since it is necessary to fold back the edges to avoid drop- 
ping lint on the surface of the film. 

The use of a machine capable of applying the cleaning liquid at a 
uniform rate under proper conditions of frictioning is therefore in the 
interest of both quality and economy. For the reasons already stated 
the operation should include inspection. Therefore, the mechanical 
aid need only carry out the cleaning proper while the film is propelled 




FIG. 



2. Modified Neumade 
machine (back). 



cleaning 



by a hand-driven rewind or a motor-driven unit, the speed of which is 
controlled by a treadle switch, as was described in an earlier paper. 2 

Modifications to a Commercially Available Machine. Cleaning 
machines are available on the market which, with some modification, 
can be made to carry on this function. Figs. 1 and 2 show the front 
and back, respectively, of the Neumade cleaner as modified for this 
purpose. It consists of a vertical main frame of cast-iron which 
supports at the front two tables covered with plush ribbon, against 
which the support and emulsion surfaces are rubbed in sequence as 
the film passes in a horizontal direction through the machine. In 



400 C. E. IVES AND E. W. JENSEN [j. s. M. p. E. 

addition, guide rolls at the point of entry and exit of the film, as 
well as spools for feeding the silk plush ribbons across the tables, 
are supported by this same frame. As sold, no provision exists for 
the continuous supply of cleaning liquid, so that either dry brushing 
or the intermittent application of the liquid can be employed. Ex- 
perience has shown that while under certain conditions the dry brush- 
ing is useful, the use of a solvent liquid is necessary to cope with 
either oily or adherent material. 

The principal modification required, therefore, was the addition 
of a reservoir and distribution system capable of supplying enough 
liquid for cleaning the largest size of roll. This was accomplished by 
installing a device commonly used to supply oil to machinery, which 
has glass walls, so that it is possible to see at all times the quantity of 
liquid in reserve and the rate at which it is delivered by the adjust- 
able needle valve. 

Below this feeder a plenum chamber was made from which tubes 
were led to the vicinity of the wiping tables through the main frame. 
A piece of wicking stuffed in the ends of these tubes has the twofold 
function of limiting the rate of flow and carrying the liquid across 
the gap between the end of the fixed distributing tubes and the ad- 
justable tables. The wicks are led into small tubular cells fastened 
to the underside of the tables where they feed the liquid to strips of 
felt which extend through slots cut in the tables. Capillarity is used 
to carry the liquid upward another one-half inch and to distribute it 
across the l 3 /g-inch width of the wiping ribbon. Adjustment of the 
wicks is easily made and seldom requires changing. As a result of 
the control exerted bV the wicks, an equal flow of liquid to the two 
tables can be maintained without any particular attention being paid 
to levelling. 

The main frame and all rollers were chromium plated with under- 
coatings of copper and nickel. It was found best to make the tables 
of stainless steel or canvas-reinforced Bakelite. 

Extensive use of the modified cleaning machine has shown that it 
can be used without danger to the film and with good economy of 
cleaning solvent. 

(2) A DUST-FREE WINDUP 

Even if the cleaning operation is entirely effective, dust particles 
are likely to be deposited on the surface of the film between the 
cleaning machine and the windup. The accumulation of an electro- 



Oct., 1940] 



LABORATORY APPARATUS 



401 



static charge, a likely occurrence if the humidity is low, aggravates 
the condition by attracting dust. Air must be supplied to the vicin- 
ity of the film as the solvent fumes are swept away into an exhaust 
duct but the cleaning pads must not be in the path of a stream of 
moist air lest moisture be condensed on them. 

The consequence of these requirements is that the film after 
leaving the cleaning machine usually passes through the air of the 
room which can not be regarded as dust-free even when great care is 
taken to keep it clean. In order to prevent winding dust particles 
into the film roll they must, therefore, be dislodged just ahead of the 
windup. 




FIG. 3. Dust-free windup. 

This dust-free winding condition was attained by enclosing a 
standard rewind in a metal box (Fig. 3) which was supplied with 
filtered air. The box was provided with a well fitting door to permit 
threading and removal of the roll and a window for observation. 
Most of the air supplied to the box was forced to escape at the open- 
ing where the film entered. Thus, a clean atmosphere was provided 
at the point of winding while the force of the escaping air swept the 
dust from the entering film. The beneficial effect was readily found in 
improved cleanliness of prints. 

The air supply in the unit illustrated was obtained by supplying 
compressed air to a compartment at one end of the box from which it 
escaped through filtering flannel into the rewind chamber. This 
arrangement was principally a matter of convenience and permitted 
carrying the unit to a number of other locations where it was used for 



402 



C. E. IVES AND E. W. JENSEN 



[J. S. M. P. E. 



determination of the possibility of eliminating dirt at the source. 
It was found that much loose dirt picked up in such operations as 
splicing could be dislodged, readily eliminating the possibility of 
abrasive action in subsequent rewinding. 

If, for any reason, it became necessary to apply more force to re- 
move firmly adherent particles, pneumatic squeegee nozzles could 
be added to the dust-free windup as shown in the drawing of Fig. 4. 



PNEUMATIC 
SQUEEGEE 
MO-Z/Z.L-EL 




DIRECT FROM 
CONDITIONED 
/MR 



FlG. 4. 



Dust-free windup with pneu- 
matic squeegee. 



(3) DARKROOM LIGHTING 

The extension of color sensitivity and the continuing advance in 
speed of motion picture negative films have reached the point where 
the general illumination of darkrooms is of little use. By far the 
greatest part of the resulting difficulty has to be met by the arrange- 
ment of work and equipment and the design of highly automatic 
machinery for film handling and for controlling conditions. Certain 
aids are available where no good substitute for visual observation is 
practicable. Two of these are described as follows : 

Meter Illumination. It is frequently desired to use meters of stand- 
ard design, such as ammeters, in darkrooms where fast panchromatic 



Oct., 1940] 



LABORATORY APPARATUS 



403 




,-g X l-j OPENING 



materials are handled. If the meter must be observed continually 
from a location near the sensitive material, the intensity of illumina- 
tion which is safe to use is wholly inadequate for accurate observa- 
tion of the meter, particularly with the parallax type which has a 
mirror and a knife-edge pointer. Even when a safelight is installed 
near the face of the meter, the illumination is still insufficient. 

Under some circumstances, it is possible to employ a visually ac- 
ceptable level of illumination if the time of exposure is limited by the 
use of a normally open switch 
operated by a push-button so 
that the light is on only mo- 
mentarily. It is preferable, 
in the interest of both con- 
venience and exposure safety, 
to maintain an acceptable 
illumination on the meter dial 
continuously, without allow- 
ing more than a small por- 
tion to reach the surround- 
ings. 

A completely safe method 
would consist of enclosing 
the meter in a hood having 
a mask, which fits closely 
to the user's face, in com- 
bination with a suitable auto- 
matic switch for cutting off 
the illumination when the 
aperture in the mask is not 
closed. Where the equipment must be used by more than one per- 
son, difficulties in design are encountered in addition to the objection 
which exists on the basis of sanitation. 

By following this general principle, but making a slight concession 
in the matter of stray light, a practical design has been realized. 
This is illustrated in Fig. 5. Essentially, it consists of a box with a 
slit in the top which is just large enough for convenient viewing but 
allows only a very small proportion of the light to escape from within. 
In the case illustrated, the meter forms the bottom of the box. The 
top is tapered to permit close access without contact with the face. 
The upper edges are rounded for safety. 



COVER 

PAINTED 
WHITE. ON 
THE. INSIDE 



LAMP 




SAFELIGHT 



FIG. 5. Illuminated meter. 



404 C. E. IVES AND E. W. JENSEN [j. s. M. p. E. 

In the present case, readings had to be made throughout a dis- 
tance of slightly over 1 inch along the scale. A slit l /& inch in width 
by I 1 / 2 inches in length was adequate. 

When a greater extent of scale must be used, observation can be 
accomplished through an arcuate slit extending along the whole scale 
or through a hole opposite the pointer axis which, of course, places 
the eye in line with the pointer, whatever the position of the latter. 

With an instrument having a broad pointer, lighting should be 
diffuse to eliminate any well defined pointer shadow. When the 
instrument is of the parallax type, the safelight or some bright area 
on the inside of the housing must be visible in the mirror at the posi- 
tion of the dial where the reading is made. 

When the view of a meter is restricted, as it is by the use of such a 
small viewing aperture, some additional care must be given to the 
matter of convenience of the viewing angle, etc. Thus, the hood 
illustrated, while of peculiar shape, fits the demands of the situation 
where it is used. Hooded meters, when viewed almost vertically 
downward, accommodate differences in stature somewhat better than 
when the direction of view is horizontal. 

(4) A METHOD OF MOUNTING SELF-LUMINOUS BUTTONS 

The "Radieye Locator" or self-luminous button, available on a 
screw mounting for use on electric wall switches, is very convenient 
in darkrooms for marking the location of indicator devices, control 
levers, door frames, the projecting edges of machines or movable 
equipment, etc. In a period of 2 minutes, visual dark-adaptation 
after leaving a light room is usually sufficient to permit seeing the 
buttons, while much longer time is needed when dependence is placed 
on a safelight. The total light spread throughout a room by the use 
of a reasonable number of the locators is almost negligible, although 
the placement should be such as to prevent the illumination of sensi- 
tive film at short range. 

In some locations the most visible area is a horizontal surface. 
When on a horizontal surface in a developing room, and particularly 
if in a protective recess, the locators are subject to chemical attack and 
are very short-lived. 

Fig. 6 shows a method of mounting luminous buttons designed to 
provide adequate protection against breakage of the button, to pre- 
vent corrosion, and to require little, if any, cleaning. The luminous 
button is screwed into a cork stopper which, in turn, is fitted tightly 



Oct., 1940] 



LABORATORY APPARATUS 



405 



into a thick glass ignition tube cut down in length, the luminous but- 
ton facing the bottom of the tube. The open end of the tube is 
sealed with oxygenated asphalt or some other corrosion-resisting 
plastic. 

To protect the sealed tube against breakage, it is mounted in a 
board placed at the desired guide point. Drain holes in the board 
prevent the accumulation of liquids around the sealed tube. 

Luminous buttons mounted as described have been used success- 
fully in a developing room where the exposure to corrosives was 
severe. 

RADIEYE LOCATOR 
PYREX IGNITION TUBE 

"" LONG, 



CORK STOPPER. 




OXYGENATED 
ASPHALT 



DRILL MOLE IN 
BOARD SLIGHTLY 
SMALL & FORCE 
TUBE INTO PLACE 



FIG. 6. A mounting for self-luminous buttons. 
(5) A FRICTION DRIVE ROLLER 

A friction drive roller for use in developing machinery, mentioned 
in a previous publication, 3 has been found adaptable and, in fact, is 
readily adjustable for use under varied conditions. In long film- 
driving trains, as in developing machines, problems arise which re- 
quire the introduction of some degree of additional drive or of braking 
action which can be furnished by such a roller. 

The obtaining of varying degrees of coupling between a roller and 
the shaft on which it is mounted is made convenient by the use of the 
design shown in Fig. 7. The outside roller dimensions are identical 
with those of the non-driving rollers. The roller is also supported 
on the shaft in the usual way and, in fact, can be converted to an idle 
roller in an instant. 



406 



C. E. IVES AND E. W. JENSEN 



[J. S. M. P. E. 



Driving engagement with the shaft is obtained through a pair of 
pressure pads which are held in contact with opposite sides of the 
shaft by the pressure applied by an arcuate stainless steel spring. 
These pads are separate from the roller but lie within apertures in 
the roller hub. When a force is applied to bring about rotation of the 
roller relative to the shaft, the friction pads are made to slide over the 
shaft surface. The resistance to sliding depends, of course, on the 
spring pressure which can be adjusted by shaping the spring as re- 
quired. The rollers do not bear on the pads radially so that the brak- 
ing force is not disturbed by the action of the roller. 

ROLLER HUB 



STAINLESS STEEL 
PIN 




SECTION A-A 

STAINLESS STEEL 
SPRINQ 

FIG. 7. A friction drive roller. 

The spring is held from slipping off by fitting it over a stainless steel 
pin in the outer surface of the pad. The surface of the pad is slightly 
crowned. No part of the driving force is applied to the spring so that 
its pressure on the pads remains constant. 

(6) A MECHANICAL FILTER FOR PRINTER DRIVING 

The design of a filter drive consisting of a flywheel and flexible 
coupling for improving the uniformity of running speed of a con- 
tinuous motion picture printer was described in a previous paper. 2 
Numerous mechanical filter designs are, of course, in use in various 
types of sound-recording and sound-reproducing equipment and have 



Oct., 1940] 



LABORATORY APPARATUS 



407 



been described in the JOURNAL. The design described in the refer- 
ence cited involved the use of a section of rubber hose for the flexible 
coupling. Damping at the coupling to suppress oscillation at the 
natural frequency of the filter system was provided only by the prop- 
erties of the hose material. 

Somewhat later, when better suppression of low-frequency oscil- 
lation was required, the hose coupling was replaced by a spider 
carrying four pairs of opposed extension coil springs which were 
packed tightly with cotton wadding to provide the required damping. 
This arrangement (Fig. 8) suggested by Dr. O. Sandvik of these Labo- 
ratories, proved satisfactory under the regular operating conditions 
with the shaft running at 90 feet per minute and was used for some 



DRIVEN PULLEY 



FLEXIBLE 

COUPLING 



FLYWHEEL 



-4 



tl I .1 FABRIC BELT 

GEAR 
II REDUCTION 



GEAR TRAIN 



TO HOLDBACK 
SPROCKET 




4= 



*C.TO FEED 
SPROCKET 



POWER TAKE-OFF 
FOR FILM TAKE-UP 

SPINDLES 



SPROCKET 

FIG. 8. Filter drive on continuous printer. 



time performing the multiple function of flexible (alignment) coup- 
ling, resilient filter member, and damping device. 

Recently it was desired to operate this machine at the much slower 
speed of 23 rpm and at the same time have, if possible, increased 
uniformity of exposure. The necessary speed reduction was ob- 
tained by a change in the ratio of pulley diameters carrying the 
woven belting which connected the precision reduction gear and the 
filter. The larger pulley mounted next to the filter was made of cast 
aluminum and was cut away to reduce the rotatory moment. The 
resulting natural frequency for the pulley-spring combination was 
thereby maintained much higher than that of the flywheel-spring 
combination so that oscillation was not aggravated too much by 
coupling of these systems. 

Studies of the motion of the printer sprocket were made by the use 
of a Strobotac and by making flash exposures through a much nar- 



408 



C. E. IVES AND E. W. JENSEN 



[J. S. M. P. E. 



rowed aperture and developing the printed film to a gamma of 4.0. 
A densitometric study of the print showed the comparative absence 
of high-frequency disturbances but the presence with both the 23 and 
90 rpm drives of a degree of oscillation at the natural frequency of the 
flywheel-spring system (about 4 cps) which was about equal in each 
case but objectionable for the intended low speed use. A disturbance 
of the same frequency and amplitude is more serious in its photogra- 
phic effect at the lower speed than at the higher because the fractional 
modulation in exposure is greater. 



SECTION --i 



SHA.FT 




KOROSE/O. STRIP 
IN PLAICE. 



SPIDER 



SHA.FT 





KOROSEfO. 
STRIPBEFORt 1 
TENSlONINfc 



CL.AMP 

FIG. 9. Modified flexible coupling. 

Since it was desired to effect the required improvement in damp- 
ing by the least extensive change in the equipment, an effort was 
made to improve the frictional damping as applied directly to the 
springs. Springs of the same type were set up separately from the 
printer and loaded with weights so as to obtain the normal deflection. 
A number of different ways of applying friction to the bodies of the 
spring were tried but it was soon found that whenever sufficient 
damping was introduced to suppress the oscillation in the desired 
degree a great increase in stiffness occurred. 

A solution was sought, therefore, in the substitution of some mate- 
rial for the springs which would have more suitable properties. Such 
a material was found in the synthetic rubber-like material, plasticized 
vinyl chloride polymer, sold under the name of "Koroseal, Grade 



Oct., 1940] LABORATORY APPARATUS 409 

116." 4 This substance has the feel and appearance somewhat like 
those of soft rubber but different mechanical characteristics. When 
it is released after stretching under tension it does not snap back in- 
stantly but returns at a rate which diminishes as the original dimen- 
sions are approached. 

This material purchased in sheet form 1 /i& inch thick was mounted 
on the spiders of the coupling as shown in Fig. 9. The spiders were 
provided with screw clamps as shown. Two 12-inch strips of the 
Koroseal, each Vie inch by 3 /ie inch in section, were threaded together 
through the open clamps, alternately passing from one spider to the 
other. The ends of the strips were secured in the clamp at the 
starting point. Then the remaining clamps were taken up, all of 
them being moved sequentially in a series of small steps so as to extend 
all portions of the strip uniformly until each clamp gripped the mate- 
rial firmly. The 12-inch length between the end fastenings effects 
about a 23-per cent stretch in the length of the strip when the radial 
distance of the seven remaining movable jaws is changed about 28 per 
cent. 

As expected from the preliminary tests the oscillation was greatly 
reduced so that uniformity of running speed and, consequently, of 
exposure time was improved in the required degree. The spider is 
not equipped with stops so that the Koroseal spring member has to 
transmit starting and stopping acceleration. The Koroseal spring is 
now used for both 23- and 90-foot-per-minute printers and, after two 
years, is judged to be sufficiently rugged for permanent use. 

REFERENCES 

1 CRABTREE, J. I., AND IVES, C. E.: "Improvements in Motion Picture Labo- 
ratory Apparatus,' ' Trans. Soc. Mot. Pict. Eng. (May, 1924), No. 18, p. 161. 

2 IVES, C. E., MILLER, A. J., AND CRABTREE, J. I.: "Improvements in Mo- 
tion Picture Laboratory Apparatus," /. Soc. Mot. Pict. Eng., XVH (July, 1931), 
p. 26. 

8 IVES, C. E.: "An Improved Roller Type Developing Rack with Stationary 
Drive," /. Soc. Mot. Pict. Eng., XXXI (Oct., 1938), p. 393. 

4 SCHOENFELD, F. K., BROWNE, A. W., JR., AND BROUS, S. L. : "Recent De- 
velopments with Koroseal," Ind. & Eng. Chem., 31 (Aug., 1939), p. 964. 

BROUS, S. L., AND SEMON, W. L.: "Koroseal A New Plastic," Ind. & Eng. 
Chem., 27 (June, 1935), p. 667. 

DISCUSSION 

MR. WILLIFORD : I think I might add a little to your description of the polym- 
erized polyvinyl chloride, known as Koroseal, by saying that in general ap- 
pearance it looks like rubber and stretches like rubber; but it is unlike rubber 



410 C. E. IVES AND E. W. JENSEN 

in that instead of coming back immediately its recovery is slower. Whether that 
is beneficial in your damping or not I do not know. When you stretch Koroseal 
you wonder whether you have stretched it past its elastic limit; but it comes 
back. It is a unique material, and I am interested in the application you have 
made of it. 

MR. IVES: That effect can not be simulated by any combination of springs or 
anything else that I know of. The property is easily demonstrated. The rate 
of return or restoration of the original dimensions in point of time is apparently 
limited. This material (No. 116} , recommended by the manufacturer, for the 
purpose, after we first worked the thing through with another type is a black 
material. Until you start pulling it, as Mr. Williford said, you might think it 
was a piece of soft rubber. The material is available in different degrees of stiff- 
ness. It has other peculiarities in its tensile properties. 

MR. KELLOGG: One of the nicest kinds of mechanical filters, if absolute 
synchronism between two machines is not required, is to run a belt around two 
large rollers between which is a pair of idlers just as you have shown. If the 
idlers are permitted to move back and forth, they will introduce the required 
flexibility for filtering, and it is especially easy in this arrangement to attach a 
suitable damping element. It makes a convenient and cheap type of filter 
which might be applicable to your case if you wanted to use it. 

MR. IVES: I suppose some of the magnetic devices described in Mr. Kellogg's 
paper might be used for this type of problem. 

MR. CRABTREE: I want to urge other members to prepare similar papers 
along these lines. All of you must have a lot of ideas stored away, none of which 
in themselves you might think big enough to justify a paper; but if each of you 
contributed only one idea a year that would be a valuable contribution to knowl- 
edge. In fact, I had in mind establishing a section of the JOURNAL for "stunts 
and gadgets." Perhaps we would not use precisely that title, but it would enable 
the engineer to publish a lot of information which at the present time, is being 
lost because he is too modest to publish it, or thinks it is not big enough to justify 
a technical paper. 



TECHNICAL NOTES 

Readers are invited to submit for publication in this section of the Journal brief 
items of technical information pertaining to the industry. 

A SYSTEM FOR REDUCTION OF 120-CYCLE MODULATION FROM A-C 
OPERATED EXCITER LAMPS* 

J. R. COONEY** 

The following is a method, applicable particularly to low-priced sound equip- 
ment and portable apparatus, for allowing the use of a-c operated exciter lamps 
with practical elimination of 120-cycle modulation effects on the reproduced 
sound. 

The system depends upon the fact that the current in a gas-filled phototube is a 
function both of the light incident upon the cathode and the potential applied to 
the anode the latter effect being due to increase in ionization of the gas atoms as 
the voltage is increased. It therefore becomes possible to compensate for periodic 




FIG. 1. 



Compensation for light variations by introduced 
a-c emf . 



variations in the exciting light by inserting, in series with the PEC anode poten- 
tial, an alternating emf having the proper phase, amplitude, and wave-form. 
(Fig. 1). Furthermore, as the effect of this a-c introduction on the PEC space- 
current depends entirely upon the number of primary electrons emitted from the 
cathode by illumination, the adjustment holds very closely for all degrees of aver- 
age illumination (as determined by a sound-track, etc., interposed between excit- 
ing light and phototube) down to zero. 



* Received July 25, 1940. 
** Waldo Theater Corp., Waldoboro, Me. 



411 



412 



TECHNICAL NOTES 



In other words, it is necessary to make only one adjustment of the balancing 
voltage say, with no film in the sound head corresponding to the percentage 
variation in illumination of the particular type of exciter lamp being used, and the 
cancellation remains substantially constant for all degrees of illumination as de- 
termined by the sound-track. 

There are various ways in which a suitable neutralizing voltage may be ob- 
tained. The unfiltered or partially filtered sections of the amplifier power-supply 



see 



O/A 





FIG. 2. Circuit employing the principle of Fig. 1. 

Ri 5,000 ohms Vz watt Ci 1 or more mfd 

R 2 500,000 ohms 1 / 2 watt C 2 0.1 mfd 

R 3 20 ohms rheostat B Bleeder 

R* 50,000 ohms 1 watt 

T 6.3-volt amplifier heater supply 

E f (01 A) ~ 3v. rms: I p ^ 2 ma. 

Exciter lamps 10-v, 7.5a; 10- v, 5a; 9-v, 4a; etc. 

contain a 120-cycle component that may be adapted, by suitable networks, for 
the purpose. 

Fig. 2 illustrates a simple circuit giving excellent results experimentally. Here 
a 120-cycle voltage of nearly perfect wave-form for the purpose is obtained by 
utilizing the space-current variations in a filament-type tube operated below tem- 
perature saturation. 

A shows a simple, direct-coupled circuit, which however has the disadvantage 
that a fair-sized bleeder is required to insure substantial independence of the d-c 
PEC potential from variations in the 01.4 circuit. This disadvantage is removed 
in 5, in which the d-c circuits are isolated. In both cases adjustment is made by 
regulating the 01.4 filament current (as the tube operates saturated it is unneces- 
sary that the filament be balanced with respect to ground) . 

This arrangement, in either case, gives a cancellation of the order of 30 db, when 
used with any of the commonly used types of exciter lamp, but has the disadvan- 
tage of being rather sensitive to power-line variations. 



CURRENT LITERATURE OF INTEREST TO THE MOTION PICTURE 

ENGINEER 



The editors present for convenient reference a list of articles dealing with subjects 
cognate to motion picture engineering published in a number of selected journals. 
Photostatic copies may be obtained from the Library of Congress, Washington, D. C., 
or from the New York Public Library, New York, N. Y. Micro copies of articles 
in magazines that are available may be obtained from the Bibliofilm Service, Depart- 
ment of Agriculture, Washington, D. C. 

American Cinematographer 

21 (September, 1940), No. 9 
Berndt's 16-Mm Sound Film Recorder Revolutionary (pp. 

389-390,430) W. STULL 

Twentieth Century Fox Holds Preview for Its Big Camera 

(pp. 396-398) W. STULL 

Constructing and Using 16-Mm Blimp for Kodachrome 
Sound (pp. 410-412) H. HUNT 

British Journal of Photography 

87 (July 26, 1940), No. 4186 
Progress in Colour (pp. 363-364) 

87 (August 9, 1940), No. 4188 
Progress in Colour (pp. 387-388) 

87 (August 16, 1940), No. 4189 
Progress in Colour (pp. 398-399) 

Electronics and Television and Short-Wave World 

13 (August, 1940), No. 150 

Frequency Characteristics of Film-Recorded Sound (pp. 
356-357), Pt. II R. H. CRICKS 

Institute of Radio Engineers, Proceedings 

28 (July, 1940), No. 7 
Acoustics in Studios (pp. 296-299) M. RETTINGER 

International Photographer 

12 (September, 1940), No. 8 
High-Speed Camera (pp. 8-9) 

Twentieth Century Camera (pp. 17-18) D. B. CLARK 

Guarding Negative Quality (p. 22) S. C. O'BRIEN 

International Projectionist 

15 (July, 1940.) No. 7 
New Lenses for Projecting Motion Pictures (pp. 7-8, 11, 

28-30) W. B. RAYTON 

Theater Sound System Optical Data (pp. 12, 15-16) R. J. KOWALSKI 

413 



414 



CURRENT LITERATURE 



Sound Track Standards Revised (pp. 17, 28), R.C.A. Sound 
Service Tools (pp. 21-22), Pt. II 

15 (August, 1940), No. 8 

Sound Screens: Structure and Function (pp. 7-8) G. F. HOLLY 

Technical Data Anent Metal Film (pp. 10, 12) R. W. CARTER 

Audience Noise vs. Volume Range (pp. 14-15, 23-26) W. A. MUELLER 

Commercialization of Non-Reflecting Surf aces (p. 16) 
The Projectionist's Interest in Auditorium Viewing Condi- 
tions (pp. 19-20) B. SCHLANGER 

Motion Picture Herald (Better Theaters Section) 

140 (August 24, 1940), No. 8 
Fitting Reproduction into the Studio-Theater Sound System 

(pp. 35-36) A. NADELL 

What Today's Sound System Must Do (pp. 37-39) W. W. SIMONS 



1940 FALL CONVENTION 



SOCIETY OF MOTION PICTURES ENGINEERS 



HOLLYWOOD ROOSEVELT HOTEL 

HOLLYWOOD, CALIFORNIA 
OCTOBER 21st-25th, INCLUSIVE 



Officers and Committees in Charge 

E. A. WILLIFORD, President 

N. LEVINSON, Executive Vice-P resident 

W. C. KUNZMANN, Convention Vice-President 

J. I. CRABTREE, Editorial Vice-President 

L. L. RYDER, Chairman, Pacific Coast Section 

H. G. TASKER, Chairman, Local Arrangements Committee 



Pacific Coast Papers Committee 

C. R. SAWYER, Chairman 

L. A. AICHOLTZ C. FAULKNER W. A. MUELLER 

O. O. CECCARINI C. N. BATSEL J. STEWART 

F. M. FALGE H. G. TASKER 

Reception and Local Arrangements 



H. G. TASKER, Chairman 



N. LEVINSON 
K. F. MORGAN 
P. MOLE 

A. M. GUNDELFINGER 

H. W. REMERSCHIED 
G. S. MITCHELL 
L. D. GRIGNON 



G. F. RACKETT 
H. W. MOYSE 
W. C. MILLER 
W. A. MUELLER 
C. L. LOOTENS 
W. V. WOLFE 
E. C. RICHARDSON 



E. HUSE 

J. O. AALBERG 

R. H. McCULLOUGH 

J. M. NICKOLAUS 

E. H. HANSEN 

R. G. LlNDERMAN 

F. M. FALGE 



Registration and Information 



W. C. KUNZMANN, Chairman 
C. W. HANDLEY J. FRANK, JR. 

S. HARRIS W. R. GREENE 



415 



416 



FALL CONVENTION 
Banquet and Dance 



[J. S. M. P. E. 



H. T. KALMUS 
E. HUSE 
L. L. RYDER 
C. DUNNING 

R. G. LlNDERMAN 



N. LEVINSON, Chairman 
G. S. MITCHELL 
P. MOLE 
H. G. TAKSER 
W. C. MILLER 

R. H. McCULLOUGH 



G. F. RACKETT 
J. O. AALBERG 
K. F. MORGAN 
H. W. MOYSE 
J. L. COURCIER 



W. C. HARCUS 
F. L. EICH 
E. M. HONAN 
H. R. LUBCKE 
W. E. THEISEN 



Hotel and Transportation 

G. A. CHAMBERS, Chairman 

L. M. HOFFMAN K. B. LAMBERT 

S. P. SOLOW F. O'GRADY 

D. P. LOYE A. C. BLANEY 

D. J. BLOOMBERG D. B. BROWN 

F. J. DURST J. G. FRAYNE 



J. O. AALBERG 
C. W. HANDLEY 
W. F. RUDOLPH 

J. M. NlCKOLAUS 
J. K. HlLLIARD 



Convention Projection 

H. GRIFFIN, Chairman 
H. A. STARKE 
L. E. CLARK 
M. S. LESHING 
A. F. EDOUART 
I. SERRURIER 



J. DURST 

R. H. McCULLOUGH 

H. W. REMERSCHIED 
H. I. REISKIND 
W. W. LINDSAY, JR. 



Officers and Members of Los Angeles Projectionists Local No. 150 



Ladies' Reception Committee 



MRS. L. L. RYDER, Hostess 
assisted by 

MRS. H. G. TASKER MRS. N. LEVINSON 
MRS. E. C. RICHARDSON MRS. P. MOLE 
MRS. G. F. RACKETT MRS. C. W. HANDLEY 
MRS. H. W. MOYSE MRS. K. F. MORGAN 

MRS. L. E. CLARK MRS. W. C. MILLER 

MRS. G. S. MITCHELL MRS. B. KREUZER 

MRS. A. M. GUNDELFINGER 



MRS. E. HUSE 
MRS. G. A. CHAMBERS 
MRS. J. O. AALBERG 
MRS. R. H. MCCULLOUGH 
MRS. C. DUNNING 
MRS. F. J. DURST 



Miss Ruth Williams, Social Director, Hollywood Roosevelt Hotel 



L. A. AICHOLTZ 
W. A. MUELLER 



Publicity 

J. HABER, Chairman 
W. R. GREENE 
G. CHAMBERS 



S. HARRIS 

A. M. GUNDELFINGER 



Oct., 1940] FALL CONVENTION 417 

New Equipment Exhibit 

B. KREUZER, Chairman 

P. MOLE F. J. DURST J. G. FRAYNE 

C. N. BATSEL O. F. NEU H. W. REMERSCHIED 

K. F. MORGAN F. M. FALGE C. R. DAILY 

P. F. HARPER G. H. WORRALL C. W. HANDLEY 

Headquarters 

Headquarters of the Convention will be the Hollywood Roosevelt Hotel, where 
excellent accommodations are assured. A reception suite will be provided for the 
Ladies' Committee, and an excellent program of entertainment will be arranged 
for the ladies who attend the Convention. 

Daily hotel rates to SMPE delegates will be as follows (European Plan) : 

One person, room and bath $ 3 . 50 

Two persons, double bed and bath 5 . 00 

Two persons, twin beds and bath 6 . 00 

Parlor suite and bath, 1 person 8 . 00-14 . 00 

Parlor suite and bath, 2 persons 12 . 00-16 . 00 

Room reservation cards, mailed to the membership early in September, should 
be returned to the Hotel immediately to be assured of satisfactory accommoda- 
tions. 

Indoor and outdoor garage facilities adjacent to the Hotel will be available to 
those who motor to the Convention. 

Members and guests of the Society will be expected to register immediately upon 
arriving at the Hotel. Convention badges and identification cards will be sup- 
plied which will be required for admittance to the various sessions, studios, and 
several Hollywood motion picture theaters. 

Railroad Fares 

The following table lists the railroad fares and Pullman charges: 

Railroad Fare Pullman 

City (round trip) (one way) 

Washington $132.20 $22.35 

Chicago 90.30 16.55 

Boston 135.00 23.65 

Detroit 106.75 19.20 

New York 135.00 22.85 

Rochester 124.05 20.50 

Cleveland 111.00 19.20 

Philadelphia 135 .00 22 . 35 

Pittsburgh 117.40 19.70 

The railroad fares given above are for round trips. Arrangements may be 
made with the railroads to take different routes going and coming, if so desired, 



418 FALL CONVENTION [J. S. M P. E. 

but once the choice is made it must be adhered to, as changes in the itinerary may 
be effected only with considerable difficulty and formality. Delegates should 
consult their local passenger agents as to schedules, rates, and stop-over privileges. 

Technical Sessions 

The Hollywood meeting always offers our membership an opportunity to be- 
come better acquainted with the studio technicians and production problems. 
Technical sessions will be held in the Blossom Room of the Hotel. Several eve- 
ning meetings will be arranged to permit attendance and participation by those 
whose work will not permit them to be free at other times. The Local Papers 
Committee is collaborating closely with the General Papers Commitee in arrang- 
ing the details of the program. 

Studio Visits 

The Local Arrangements Committee is planning visits to several studios during 
the Convention week. Details will be announced in the Programs. Admittance 
to the studios will be by registration card or Convention badge only. 

New Equipment Exhibit 

An exhibit of newly developed motion picture equipment will be held in the 
Bombay and Singapore Rooms of the Hotel, on the mezzanine. Those who wish 
to enter their equipment in this exhibit should communicate as early as possible 
with the General Office of the Society at the Hotel Pennsylvania, New York, N. Y. 

Semi-Annual Banquet and Dance 

The Semi-Annual Banquet of the Society will be held at the Hotel on Wednes- 
day, October 23rd, in the Blossom Room. A feature of the evening will be the 
annual presentations of the SMPE Progress Medal and SMPE Journal Award. 
Officers-elect for 1941 will be announced and introduced, and brief addresses will 
be delivered by prominent members of the motion picture industry. The eve- 
ning will conclude with entertainment and dancing. 

The Informal Get-Together Luncheon will be held in the Florentine Room of 
the Hotel on Monday, October 21st, at 12:30 P. M. 

Motion Pictures 

At the time of registering, passes will be issued to the delegates to the Conven- 
tion, admitting them to the following motion picture theaters in Hollywood, by 
courtesy of the companies named: Grauman's Chinese and Egyptian Theaters 
(Fox West Coast Theaters Corp.), Warner's Hollywood Theater (Warner Brothers 
Theaters, Inc.), Pantages Hollywood Theater (Rodney Pantages, Inc.). These 
passes will be valid for the duration of the Convention. 

Ladies' Program 

An especially attractive program for the ladies attending the Convention is 
being arranged by Mrs. L. L. Ryder, hostess, and the Ladies' Committee. A suite 



Oct.. 1940] FALL CONVENTION 419 

will be provided in the Hotel, where the ladies will register and meet for the 
various events upon their program. Further details will be published in a suc- 
ceeding issue of the JOURNAL. 

Points of Interest 

En route: Boulder Dam, Las Vegas, Nevada; and the various National Parks. 

Hollywood and vicinity: Beautiful Catalina Island; Zeiss Planetarium; Mt. 
Wilson Observatory; Lookout Point, on Lookout Mountain; Huntington Library 
and Art Gallery (by appointment only) ; Palm Springs, Calif. ; Beaches at Ocean 
Park and Venice, Calif.; famous old Spanish missions; Los Angeles Museum 
(housing the SMPE motion picture exhibit); Mexican village and street, Los 
Angeles. 

In addition, numerous interesting side trips may be made to various points 
throughout the West, both by railroad and bus. Among the bus trips available 
are those to Santa Barbara, Death Valley, Agua Caliente, Laguna, Pasadena, and 
Palm Springs, and special tours may be made throughout the Hollywood area, 
visiting the motion picture and radio studios. 

Those who wish to visit San Francisco may arrange for stop-over privileges 
when purchasing their railroad tickets. Arrangements have been made with the 
Hotel Mark Hopkins for single accommodations for $5 daily and double with twin 
beds for $7, both with baths. The Fairmont Hotel also extends a rate of $4 single 
and $6 double, with bath. Reservation may be made by writing directly to the 
Hotel. 

W. C. KUNZMANN, 
Convention Vice-President 



ABSTRACTS OF PAPERS OF THE 

FALL CONVENTION 

AT 

HOLLYWOOD, CALIF. 

OCTOBER 21-25, 1940 

The Papers Committee submits for the consideration of the membership the follow- 
ing abstracts of papers to be presented at the Fall Convention. It is hoped that the 
publication of these abstracts will encourage attendance at the meeting and facilitate 
discussion. The papers presented at Conventions constitute the bulk of the material 
published in the Journal. The abstracts may therefore be used as convenient refer- 
ence until the papers are published. 

J. I. CRABTREE, Editorial Vice-P resident 

S. HARRIS, Chairman, Papers Committee 

C. R. SAWYER, Chairman, West Coast Papers Committee 

L. A. AICHOLTZ F. M. FALGE F. H. RICHARDSON 

P. ARNOLD R. E. FARNHAM W. H. ROBINSON 

C. N. BATSEL C. FAULKNER C. R. SAWYER 

L. N. BUSCH C. FLANNAGAN J. STEWART 

O. O. CECCARINI L. D. GRIGNON H. G. TASKER 

G. A. CHAMBERS E. W. KELLOGG R. TOWNSEND 

A. C. COOK G. E. MATTHEWS P. R. VON SCHROTT 

L. J. J. DIDIEE R. F. MITCHELL I. D. WRATTEN 

A. C. DOWNES W. A. MUELLER C. K. WILSON 
W. H. OFFENHAUSER 

Black Light for Theater Auditoriums; H. J. Chanon, General Electric Co., 
Cleveland, Ohio, and F. M. Falge, General Electric Co., Los Angeles, Calif. 

The demand for near-ultraviolet radiation, commonly called "black light," in 
the production of fluorescent effects has shown the need for a technical approach 
to the problem. New technics of measurement as well as design information, 
data on sources and material are necessary to insure most effective use of these 
new media. 

The paper covers design information on the lighting of fluorescent carpet, deco- 
rative wall and ceiling murals, and other decorative applications. Information 
on light-sources, standard niters for absorbing the visible light emitted by the 
sources, as well as response characteristics of various types of fluorescent materials 
have been obtained. The effect of extraneous visible light in masking the bright- 
ness of the fluorescent material is discussed. One convenient method of measur- 
ing the near-ultraviolet energy from mercury light-sources in existing installations 
is explained. 

Acoustic Design Features of Studio Stages, Monitor Rooms, and Review 
Rooms; D. P. Loye, Electrical Research Products, Inc., Hollywood, Calif, 
420 



ABSTRACTS OF CONVENTION PAPERS 421 

A survey was made of studio experience, as one step in the determination of the 
most nearly ideal design characteristics practicable for studio stages, review 
rooms, and other units. Acoustic measurements were also made of Hollywood 
studio units of these types. These data were correlated with the information 
obtained in the survey, and used as a valuable guide in the determination of the 
optimum characteristics and dimensions recommended for major studio scoring 
stages, monitor rooms, dubbing rooms, review rooms, and studio theaters. 

These data are described in detail, and recommendations regarding the studio 
units are given. These recommendations include the optimum reverberation and 
other acoustic characteristics, and also the most practicable sizes which experience 
and theoretical considerations indicate to be desirable. 

Information regarding Hollywood preview theaters is included in an appendix. 

Stability in Synchronous Motors; S. Read, Jr., and E. W. Kellogg, RCA Mfg. 
Co., Inc., Camden, N. J. 

For the most part, since the advent of talking pictures, motors have been em- 
ployed whose performance is above reproach. The various types of motor, 
however, differ widely in their ability to resist load irregularities and in their 
tendency to oscillate when a disturbance occurs. For the more critical applica- 
tions these factors deserve careful consideration when the type or design is 
being selected. The principal types of synchronous motor are (2) the variable- 
reluctance or induced-pole motor, (2) the separately excited motor, (5) the ac-dc 
motor, (4) the hysteresis motor, (5) the low-speed multi-tooth motor (of the type 
used for electric clocks), (6) the polyphase, uniform torque modification of 
number 5, and (7) selsyn motors. 

Many of the characteristics of synchronous motors may be best understood 
by assuming that the polyphase winding produces a uniformly rotating magnetic 
field, but estimating the stiffness and stability demands a knowledge of the 
manner in which the a-c input varies with mechanical displacement. Generous 
pole-face grids are essential for stability. Ac-dc motors have certain elements 
of instability as well as stabilizing factors, which are not present in straight 
synchronous motors. The magnitude of these effects can to some extent be 
controlled by the external circuit arrangements. Selsyn motors are less readily 
damped than regular synchronous motors, and for this reason arrangements by 
which the synchronous motors can be interlocked from standstill are of interest. 

Ground-Noise Reduction Systems; E. W. Kellogg, RCA Manufacturing Co., 
Camden, N. J. 

The principal purpose of the paper is to formulate a statement of the desired 
characteristics of a ground-noise-reduction system, in terms of such factors as 
prompt opening, peak reading, and filtering. In this it is assumed that anticipa- 
tion is not employed. It is desirable to limit the filtering to a single stage of re- 
sistance-capacity filtering (or equivalent) . Slow closing helps filtering and peak 
reading. The better the peak reading properties of the circuit, and the less the 
filtering delay, the smaller can the margins be made without causing too frequent 
clipping. 

A number of circuits are discussed which have been proposed for improving the 
filtering without sacrifice of quick opening, or reasonably rapid closing. 



422 ABSTRACTS OF CONVENTION PAPERS [J. S. M. P. E. 

ID some operations, anticipation is entirely practical, and if this is done it ap- 
pears possible to provide an almost perfect envelope current. 

Editing a Motion Picture; I. J. Wilkinson and W. Hamilton, RKO Radio 
Pictures, Inc., Los Angeles, Calif. 

The paper is an attempt to reduce to words a portion of the mechanical and 
artistic elements involved in the process of editing a motion picture. The authors 
realize that they are dealing with a highly controversial subject but feel that, as 
there is so little pertinent material available on this phase of motion picture 
production, this paper may serve as a preliminary to a study on a larger scale. 

Consideration is given to the origin of film editing and its advancement from 
the purely mechanical craft of the early days to its present status as a contributing 
factor in the entertainment and dramatic values of the motion picture of today. 

Demonstration film is presented to illustrate various editing technics and to 
show the possibility of their use as a means of drastically altering original story 
and dramatic conception. 

Line Microphones; H. F. Olson, RCA Manufacturing Co., Camden, N. J. 

A line microphone is a microphone consisting of a large number of small tubes 
with the open ends, as pick-up points, equally spaced along a line and the other 
ends connected by means of a common junction to a transducer element for con- 
verting the sound vibrations which converge upon the junction into the corre- 
sponding electrical variations. Several types of line microphones with the useful 
directivity along the line axis are described as follows : a simple line, a line with 
progressive delay, and two lines with progressive delay and a pressure gradient 
element. 

A Line Type of Microphone for Speech Pick-up; L. J. Anderson, RCA Manu- 
facturing Co., Camden, N. J. 

The development of a line type of microphone is discussed, having directional 
characteristics which are relatively independent of frequency, and which are 
of such size as to be readily portable. Uniform directional characteristics are ob- 
tained by constructing the line in such a way that the effective length becomes less 
with increasing frequency. Physical size limitations are largely responsible for 
confining the microphone to speech pick-up applications. 

A Method of Calibrating Microphones; F. L. Hopper, Electrical Research Prod- 
ucts, Inc., Hollywood, Calif., and F. F. Romanow, Bell Telephone Laboratories, 
New York, N. Y. 

Methods of determining the performance characteristics of microphones by 
acoustic measurements are described. Factors involving the accuracy of the 
methods are discussed. The correlation between a microphone's performance as 
determined by acoustic measurement and by listening tests is reported. Applica- 
tion of both types of test to a studio type of cardioid microphone is given as an 
example. 

General and Design Considerations of Low-Noise Microphones; A. L. Williams 
and H. G. Baerwald, The Brush Development Co., Cleveland, Ohio. 



Oct., 1940] ABSTRACTS OF CONVENTION PAPERS 423 

With the development of the microphone art toward increased fidelity, thermal 
agitation noise becomes the principal limitation and therefore a major problem. 
Its physical side has been discussed in a recent publication where the factors on 
which noise performance depends have been analyzed, and a suitable noise rating 
based on aural perception has been proposed. The purpose of this paper is to out- 
line some practical consequences. Different microphone types are discussed in 
regard to their noise performance and, particularly, to their inherent limitations of 
noise reduction. Multiple piezoelectric microphones which lend themselves par- 
ticularly well to the design of quiet units, are treated in more detail. The noise 
performance of different sound-cell types is given including a recent develop- 
mental unit which tends to realize the inherent efficiency of the piezoelectric type 
of microphone to a fuller extent. The practical realization of the qualities of 
piezoelectric units in a microphone depends on a suitable choice of the associated 
circuits and tubes; the principles and limitations of their design are indicated. 
Application is also made to the design of minimum-noise combinations of different 
microphone types, particularly to an adjustable-hypercardioid (unidirectional) 
combination of ribbon and sound-cell type. Some performance data of a corre- 
sponding experimental model are given. 

A 200-Mil Variable-Area Modulator; R. W. Benfer and G. T. Lorance, Elec- 
trical Research Products, Inc., Hollywood, Calif. 

A modulator using a new vibrating-mirror unit has been developed for recording 
double-width variable-area sound-track. The noise-reduction shutter is at the 
slit, making it possible to record, with noise reduction, Class A push-pull track 
comprising two standard bilateral tracks, one of which is located in accordance 
with the dimensional standards for single track. While this has been its principal 
use to date, it is readily adaptable for other types of track. A visual monitor 
shows operation of the noise-reduction shutter and the amplitude of signal modu- 
lation in both directions from the base-line with a positive indication of peak, over- 
load. An exposure meter is included to serve as a check on lamp current and 
track balance. The light-source is a tungsten filament lamp which will properly 
expose fine-grain emulsions to "white" light or standard emulsions through an 
ultraviolet filter. 

An Investigation of Some Factors Influencing Volume Range in Photographic 
Sound Recording; W. K. Grimwood and O. Sandvik, Eastman Kodak Co., 
Rochester, N. Y. 

This is an extension of an earlier investigation of background noise. The 
present paper deals more specifically with the relation between volume range and 
the type of photographic materials and the sensitometric conditions used. A 
brief study of the effect of the spectral quality of the radiation used in recording 
and printing is included. 

Measurement of Photographic Printing Density; J. G. Frayne, Electrical 
Research Products, Inc., Hollywood, Calif. 

When the spectral sensitivity of positive film is simulated by the use of a suit- 
able combination of phototube and optical filter in the integrating sphere densi- 
tometer, the printing density of any type of negative, irrespective of grain size, with 



424 ABSTRACTS OF CONVENTION PAPERS [J. S. M. P. E. 

any type of base or backing, may be accurately determined. Printing density is 
practically independent of the type of light-source or filtering employed in the 
printer. Relationships between printing and visual diffuse densities for various 
types of negatives have been established. 

Stabilized Disk Record Cutters; S. J. Begun, The Brush Development Co., 
Cleveland, Ohio. 

Where it is desirable to obtain good quality in disk recording, the cutter used 
must have a wide frequency range and a low content of harmonic distortion. 
Furthermore, care must be exercised that the sensitivity of such a cutting device 
should not be affected by temperature changes. This is particularly important 
in case the recording equipment, for some reason, does not work in air-conditioned 
rooms. 

The sensitivity, as well as the amount of harmonic distortion generated for 
magnetic and crystal cutters, depends upon the temperature. In a magnetic 
cutter, the characteristic of the damping material varies sufficiently with tem- 
perature change to require constant temperature conditions. With respect to 
a crystal cutter, it has been found that a crystal element will drive a recording 
stylus with negligible distortion if its temperature is of the order of 30 C or above. 
For this reason, a crystal cutter has been developed with a built-in thermostat 
to control a heating element, which will keep the cutter temperature constant 
within narrow limits. 

The design of such a cutter and the performance characteristic are described 
in detail. The high degree of stability of such a temperature-controlled cutter is 
shown. 

A Portable Disk Recording-Reproducing Machine; J. C. Davidson and C. C. 
Davis, Electrical Research Products, Inc., Hollywood, Calif. 

The R A-280 equipment is intended as a portable high-quality disk recording 
and reproducing machine. It was designed primarily to include a feed-back re- 
corder, a vertical and lateral reproducer, and an amplifier with equalizers and 
suitable switching arrangement for recording or reproducing. 

The turntable drive includes an electrically and mechanically balanced motor, 
a precision worm and gear, and an oil damped mechanical filter. Vibration is 
prevented from reaching the turntable by a bellows type coupling. The filter 
consists of a reed-type spring surrounded in oil and provided with suitable linkage 
to the turntable. 

It is felt the electrical and mechanical requirements for a high-quality machine 
have been met. The frequency flutter has been maintained at ==0.03 to =*=0.06 
per cent and mechanical-noise pick-up is below the threshold of feeling and shows 
no optical pattern in the recording. 

An Improved Playback Horn Equipment; G. R. Daily, Paramount Pictures, 
Inc., Hollywood, Calif. 

A dolly-mounted, high-quality two-way horn system for playback and announc- 
ing service on production recording stages is described. A reflex-type horn cabi- 
net is mounted on a four-wheel steerable dolly, together with a 50-watt amplifier 
and cable reel. The horn unit can be rotated on the dolly to direct it at the ac- 



Oct., 1940] ABSTRACTS OF CONVENTION PAPERS 425 

tion, or be readily removed from the dolly for use on parallels, or suspended from 
ceiling girders. An extension connection is provided for a W.E. 750-A speaker 
for low-level direct recording of playbacks. An extension director cut-out horn 
control is provided. The mixers' playback control box provides, (a) mixing from 
any two of four film or disk input positions; (b) extensions for cueing by phone 
monitored by the director or actors; (c) connections for portable disk recording 
from a bridging circuit across the film recording main amplifier output, and (d) 
film recording connection from the playback circuit. 

Improved Motor Drive for Self-Phasing of Process Projection Equipment; 
H. G. Tasker, Paramount Pictures, Inc., Hollywood, Calif. 

Process projection photography requires that the shutter of the projector and 
that of the camera open and close simultaneously. The relation between the 
shutter speeds and the pole frequencies of normal motion picture motor systems 
is such that there may be one, four, or five incorrect shutter relationships for each 
correct one, if the motors are interlocked at random. Earlier methods of insuring 
correct phasing between camera and projector shutters did not take proper ac- 
count of the economic importance of fast and reliable operation. This paper 
presents the results of a time and economic study indicating savings of many 
thousands of dollars annually per studio, accruing from the use of a motor system 
which automatically phases the shutters of camera and projector, and which has 
a very high degree of reliability. The design and performance features of such a 
motor system are described in their relation to earlier efforts along this same line, 
together with a report on three months' production use on the new system. 

Twentieth Century Camera; G. Laube, Twentieth Century- Fox Film Corp., 
Hollywood, Calif. 

Offering a means for cutting costs of production and fitting admirably hi the 
picture of modern streamline equipment, the new Twentieth Century Silenced 
Camera recently made its official debut to an assembly of cine-technicians and 
cameramen. Although the camera was designed primarily to reduce noise, it also 
embodies many of those conveniences and devices which spell speed and aid in cost 
cutting. 

The camera has been designed and built along new principles and, instead of 
trying to hold the noise in the camera case or the blimp, the noise has been reduced 
at its source to the end that the fast-moving reciprocating parts are as light and as 
small as possible and when assembled yield uniform acceleration and deceleration, 
with a resultant optimum movement of the film and a reduction in noise-making 
vibration. This, when coupled with a patented sound insulating mount for the 
film moving mechanism, reduces the noise output to a level substantially equiva- 
lent to the noise level of the best blimped camera available. Other features in- 
cluded in the camera are described in the paper. 

Electrooptical Slating and Cueing Device; D. B. Clark, Twentieth Century-Fox 
Film Corp., Hollywood, Calif. 

As a direct result of the necessity of reducing budgets and cutting corners in 
motion picture production, many labor-saving devices have lately become evident 
in the studios. Among the more important of these is a new slating device de- 



426 ABSTRACTS OF CONVENTION PAPERS [J. S. M. P. E. 

veloped and used by the camera department of the Twentieth Century-Fox 
studios. 

Designed mainly to save time and film and to put bigger and better slates on the 
film, the device is a complete unit comprising its own optical system, its own 
illumination, and carries means for mounting various changeable indicia. These 
are all assembled in a small casing adapted to be swung into and out of a photo- 
graphing position a few inches in front of the camera lens to slate the film in the 
camera. When not in use, the device hangs inconspicuously beneath the sun- 
shade, where it is readily accessible for changing the indicia for successive shots 
and is easily swung into slating position by a simple twist of the wrist by the 
camera operator. When using the slating device in production, the camera case 
need not be opened for cueing and marking takes. This is done photographically, 
and the film ordinarily wasted by needless exposure is saved for use. 

One of the novel features resides in the indicia carrier member which is designed 
to provide a smooth flat field, including the changeable numbers to yield a clean- 
cut reflection when the indicia are projected upon the film, said carrier member 
being readily removable from the casing for changing the data. 

In operation the device is swung into a photographing position within the sun- 
shade directly in front of the camera lens before the camera starts turning and, 
since the device itself blocks off all light except the illuminated indicia, the first 
frame of the slate can be used as a synch, mark or a cue mark. Under this ar- 
rangement, the slating indicia would be photographed on the film while the camera 
was coming up to speed, thus saving film which is ordinarily lost. Provision is 
made for operating the illuminating light either from a battery or the 220 a-c that 
drives the camera motor, the light being controlled by a switch that automatically 
cuts in as the device is moved into a photographing position. 

Photoelectric Method of Rating the Light-Speeds of Lenses; D. B. Clark, 
Twentieth Century- Fox Film Corp., Hollywood, Calif. 

Photographers and cinematographers have realized for some time that some- 
thing was wrong with the present method of calibrating light-stops on lenses. As 
various makes of lenses were interchanged on shots throughout the making of a 
motion picture, it became more and more obvious that the// rating did not repre- 
sent a true value of the light-transmitting capacity of the lens. As a result the 
real tough job of a cameraman has been to match negative densities in a procession 
of shots that have been made on lenses of different makes, different focal lengths, 
and different stops. Even though the lenses are rated as to light-speed and cali- 
brated under the // system, it is still a guessing game, since some of these ratings 
are as much as one hundred per cent in error when reduced to actual transmitting 
capacity of the lens. Since the // system is the only system used at present for 
rating the light-speed of lenses, cameramen have been forced to use this system 
but have found that it is merely a guide and can not be depended upon where 
accuracy is required. In view of all this, it is believed that a system for rating the 
light-speed of all lenses based upon actual light transmitted through the lens, re- 
gardless of make, size, or any other physical characteristic of the lens, should be of 
value not only to lens makers, to give them a reading on the overall efficiency of 
the lens, but also to the cinematographer, to give him an actual effective rating as 
to the light-valving capacity of the lens. 



Oct., 1940] ABSTRACTS OF CONVENTION PAPERS 427 

Such a system has been used in rating all lenses in the camera department of 
this studio. Disregarding all physical dimensions or characteristics, each lens in 
the department was calibrated according to the actual value of effective light 
transmitted with respect to a predetermined reference base. The reference base 
was established by measuring the effective light transmitted through a 35-mm 
lens set at//3.2, the source of light being a uniformly lighted field of fixed inten- 
sity. This same field was used as the source of light for all lens calibrations. 
The result was a lens system wherein a light-speed rating represents the same 
amount of light regardless of make or size of the lens and where the different light- 
stops on the different lenses indicate a true proportional value of the basic light. 

A New Treatment for the Prevention of Film Abrasion and Oil Mottle; R. H. 
Talbot, Eastman Kodak Co., Rochester, N. Y. 

A new type of lacquer has been devised which may be simply and rapidly ap- 
plied to either one or both sides of 16- and 35-mm films and which may be readily 
removed in ordinary processing equipment by the use of carbonate solution. The 
function of the lacquer is to absorb all the ordinary cinch marks and other abra- 
sions commonly found on cine films which have been in service in the trade. 
Tests hi the field have indicated that the lacquer is somewhat more resistant to 
abrasion than are the normal film surfaces. When the lacquer has been removed 
and replaced with a fresh coat, the film is found to be in essentially as good condi- 
tion as when new. The lacquer is useful in protecting negatives, master positives, 
duplicating negatives, and prints from all ordinary abrasions. In addition, the 
lacquer because of its glossy surface eliminates the mottle or flicker on the screen 
due to oil on the film. 

Report of the Committee on Preservation of Film; J. G. Bradley, Chairman. 

A statement of the work of the Committee as a whole and individual reports of 
sub-committees on the following subjects: (1) handling and winding of film; 
(2) safe and economical storage, size of vent per unit weight of film determined, 
microfilm testing methods developed; and (3) printers for old and shrunken film. 

Production Quality Sound with Single System Portable Equipment; D. Y. 
Bradshaw, March of Time, New York, N. Y. 

The March of Time requires equipment of great portability and simplicity of 
operation, yet retaining good quality. By using Class B push-pull, variable-area 
recording, a complete noise-reduction sound system weighing fifty pounds was 
obtained. This single system was used in production of the feature picture The 
Ramparts We Watch. Problems arise from (1) recording on panchromatic 
negative, (2} lack of control over negative processing, (3) instability of recording 
unit caused by rough use of camera on which it is mounted, and (4) distortion 
due to lateral track shift. Means for overcoming these handicaps sufficiently 
have been found. Single system can be used without great sacrifice in quality, 
where time and space are factors. 

Some Laboratory Problems in Processing 16-Mm Sound with Black-and- 
White and Color Films; Wm. H. Offenhauser, Jr., Precision Film Laboratories, 
New York, N. Y. 



428 ABSTRACTS OF CONVENTION PAPERS [J. S. M. P. E. 

The duplication of 16-mm films involves many relatively intricate problems 
not encountered in the laboratory processing of 35-mm sound-films. These 
problems have given rise to procedures and apparatus radically different from 
those in use in 35-mm. 

The two major differences that are especially significant are (1) the use of 
reversal for original films; (2) the existence of but one row of sprocket-holes on 
the 16-mm sound-film. 

It is interesting to note that all our present standards in 16-mm blindly assume 
the negative-positive method of operation, ignoring entirely the reversal and 
Kodachrome. At the present time even the emulsion position of the 16-mm 
film is standardized on the basis of a 35-mm sound negative and 35-mm picture 
negative as originals. As a result, our 16-mm dimensions so derived from 35-mm 
are inconsistent with the projector dimensions at present in use, and inconsistent 
with the pressing needs arising from the direct 16-mm field. 

Much of the difficulty arises from the rather obvious lack of concern displayed 
by the 35-mm entertainment industry and the very rapid simultaneous growth of 
direct 16-mm in educational and industrial applications especially in connection 
with the duplication of sound on Kodachrome. 

Some of the special processes and special apparatus features involved are de- 
scribed which have made possible workable solutions to the problems involved. 

Reduction of Sprocket-Hole Modulation hi Film Processing; M. Leshing, T. 
Ingman, and K. Pier, Twentieth Century- Fox Film Corp., Hollywood, Calif. 

One of the contributing factors to sound-track degradation is sprocket-hole 
modulation. This is probably more commonly known as 96-cycle modulation and 
results from non-uniform action of developer around the perforation holes during 
the time of processing. Its chief remedy is turbulation. 

The practical aspects of controlling the amount of sprocket-hole modulation is 
described herein. Curves showing the increase of this distortion due to diminished 
turbulation are included as well as those showing the intermodulation of recorded 
sound by sprocket -hole agitation. Photographs showing various types of sprocket- 
hole modulation are also presented. There are also shown samples of modula- 
tion contributed by developing machines through mechanical defects, such as 
pressure created by binding rollers and mechanical frictions introduced in the proc- 
essing machine proper. A complete description of the turbulation methods em- 
ployed at the Film Laboratory of Twentieth Century-Fox Film Corporation at 
Hollywood is disclosed and the various sensitometric means of control relative to 
this problem are given. 

Some Observations on Latent Image Stability of Motion Picture Film; K. 
Famulener and E. Loessel, Agfa Ansco Corp., Binghamton, N. Y. 

The observations reported are the result of an investigation to determine defi- 
nitely the effect of a delay between the exposure and development of modern mo- 
tion picture films. The stability of the latent image hi terms of speed, gradation, 
graininess, and color response has been studied. 

In general, a definite speed increase was noted on negative emulsions, a decrease 
on positive emulsions. There were also changes hi gradation and graininess. 
The detailed findings, which vary considerably with the individual emulsion type 



Oct., 1940] ABSTRACTS OF CONVENTION PAPERS 429 

are given, followed by a general discussion and interpretation of the results. A 
brief review of the literature is included. 

Fixing Baths and Their Properties; J. I. Crabtree, H. Parker, and H. D. 
Russell, Eastman Kodak Co., Rochester, N. Y. 

In addition to removing the unreduced silver halides from an exposed and 
developed emulsion, the fixing bath should (a) arrest development immediately, 
and (6) harden the gelatin film so as to prevent excessive swelling during washing 
and reduce mechanical injury during handling. 

The fixing agent usually consists of sodium or ammonium thiosulfate, or a 
mixture of sodium thiosulfate with ammonium chloride. The bath also contains 
an acid (usually acetic acid) to arrest development, sodium sulfite which inhibits 
the precipitation of sulfur, and potassium or chrome alum which tans the gelatin. 

The addition of developer carried into the fixing bath tends to cause the pre- 
cipitation of aluminum sulfite but this can be prevented by (a) revival of the bath 
with acid at intervals, or (b) the addition of boric acid which also extends the 
pH range over which effective hardening is obtained. The exhaustion point at 
which revival should occur may be determined with H indicators. 

Various fixing bath formulas are included and their properties discussed in 
terms of (a) developer capacity, (b) sludging and scumming propensity, and 
(c) hardening life. 

The Effect of Developer Agitation on Density Uniformity and Rate of Develop- 
ment; C. E. Ives and E. W. Jensen, Eastman Kodak Co., Rochester, N. Y. 

A number of essentially different methods of developer agitation of interest 
in motion picture work have been studied experimentally. In one case the 
film was held against the inside wall of a conduit through which the developer 
was pumped at predetermined velocities so as to maintain the required conditions 
of turbulent flow. By mounting a loop of film on a pair of rollers, the effect of 
variation in running speed of the film was studied. Tests were made of the 
effectiveness of liquid jets and also of wringers and scrapers for periodic renewal 
of developer at the emulsion surface. In order to determine the relative im- 
portance of different degrees of developer agitation and of developer renewal by 
the process of unaided diffusion, the rate of development was varied widely by 
adjustment of the developer formulas. 

Negative Exposure Control; D. Norwood, Hollywood, Calif. 

It would be desirable to have negative exposure control on the basis of an exact 
science. Toward this end the functioning of the human eye as it views a photo 
subject, and then the photographic reproduction of the subject, is studied. The 
brightness of the photo subject is broken down into its components of reflectance, 
a constant, and incident illumination, a variable. The mechanism of the eye acts 
to compensate for changes in the variable incident illumination. Recognition of 
the tone of the object is based on its fixed property of reflectance. It is this con- 
stant that determines the print density used to portray the object. Between the 
subject's fixed reflectance and the print's fixed density lies the variable of negative 
density. A system is proposed whereby a given reflectance hi the subject is repre- 



430 ABSTRACTS OF CONVENTION PAPERS [J. S. M. p. E. 

sented by a fixed density in the negative. Many advantages derive from this 
system. Operation of the system involves negative exposure control by means of 
measurement of incident light. Measurement of effective incident illumination is 
best accomplished by means of a photoelectric meter specifically designed to re- 
spond to the three dimensional characteristics of incident illumination. The sys- 
tem described is free from many of the influences which tend to cause undesirable 
variations and errors in negative exposure. It provides a means of putting nega- 
tive exposure control on the basis of an exact science. 

Hollywood's Low-Temperature Sound-Stage; R. Van Slyker, Los Angeles, 
Calif. 

The California Consumers Corporation, of Los Angeles, set aside one of its large 
ice storage buildings to introduce to the studios a new method of making realistic 
snow scenes. 

The purpose of the ice storage building was to furnish a low-temperature sound- 
stage, where water ice could be used for snow, and enable the casts breath to be- 
come visible, as actually occurs in cold or wintery climates. 

Snow is manufactured on the low-temperature sound-stage by means of 
specially constructed portable blowers, grinding 50-pound blocks of ice and ex- 
pelling through suitable nozzle a fine, aerated snow, directed to the set where and 
when needed. 

The introduction of Technicolor to the low-temperature sound-stage created 
many new problems in ventilation, due to the low temperature of the atmosphere 
and quantity of air movement needed to remove gases and smoke from the stage 
during shooting periods. 

The unusual heat load requirements necessitated the construction of external 
bunker systems, to augment the existing refrigeration for color production. 

This was accomplished by the combined use of water ice and ammonia refriger- 
ation in these bunkers, giving a total refrigerating capacity of approximately 650 
tons in the system to chill 64,000 cfm of fresh air to 20 F. 

NBC Television Covers the Republican National Convention of 1940; H. P. 

See, National Broadcasting Co., New York, N. Y. 

Television transmission facilities were installed at the Republican National Con- 
vention of 1940 held at Convention Hall, Philadelphia, June 24th to 28th. This 
marked the first time that a news event of national importance, transpiring at a 
point greater than twenty -five miles distant from New York City, was successfully 
televised and viewed by NBC's television audience in the New York Metropolitan 
Area. Program transmission was continuously maintained during each of five 
daily sessions. These transmissions totaled thirty-three hours and seventeen 
minutes. 

This paper describes the method by which the National Broadcasting Company 
originated the television pictures at Philadelphia and transmitted them through 
the facilities of the Bell System to New York, where they were radiated from 
Station W2XBS, the television transmitter atop the Empire State Building tower. 
The signals from New York were received by the General Electric Company by 
means of a specially constructed receiving system near Schenectady and re-trans- 
mitted on Station W2XB to the television audience in that vicinity. The audi- 



Oct., 1940] ABSTRACTS OF CONVENTION PAPERS 431 

ence consisted of approximately 40,000 persons scattered throughout New York, 
New Jersey, and Connecticut. 

The equipment and its functions are described. Reference is made to the mode 
and continuity of operation as distinguished from newsreel participation at the 
same event. 

Problems in Television Image Resolution; C. F. Wolcott, Gilfillan Bros., 
Inc., Los Angeles, Calif. 

This paper is primarily thought-provoking, and states problems involved in 
the consideration of suitable standards now before the National Television Sys- 
tems Committee. 

Resolution is discussed from a standpoint of the number of lines and fields 
within the limits of presently assigned channels. Related problems touched 
upon are flicker frequency vs. illumination, and some of the difficulties which 
must be guarded against with colored images, such as raster displacement occa- 
sioned by superimposed extraneous magnetic fields or voltages. 

The effects of motion, which tend to smear detail, are discussed in relation to 
frame and field frequency. 

The major limitations of present scanning-spot shape and intensity distribution, 
which determine the vertical and horizontal widths of confusion, have been re- 
moved in the laboratory, introducing the possibility of markedly improved 
definition with a given number of lines and fields which must be reckoned with 
in determining standards. 



SOCIETY ANNOUNCEMENTS 



1940 FALL CONVENTION AT HOLLYWOOD 

Details of the Convention to be held at Hollywood, October 21st-25th, are 
given in the preceding section of this issue of the JOURNAL. Members of the 
Society are urged to make every effort to attend as a very interesting program 
is being arranged and a number of studio visits and other attractions of a tech- 
nical as well as entertaining nature are being planned. 

PROPOSED AMENDMENTS OF THE BY-LAWS 

In the preceding issue of the JOURNAL (September, p. 323) were published 
several proposed amendments to be acted upon by the Society at the approaching 
Hollywood Convention, October 21st. 

With respect to the proposed By-Law XI, Sec. 4, relating to officers, an in- 
accuracy in the wording makes it advisable to repeat the amendment in its 
correct form, viz.: 

BY-LAW XI, SEC. 4, OFFICERS 

Present Wording. Each Section shall nominate and elect a chairman, two 
managers, and a secretary-treasurer. The Section chairman shall .... 

Proposed Wording. The officers of each Section shall be a chairman and a 
secretary-treasurer. The Section chairmen shall automatically become members 
of the Board of Governors of the General Society, and continue in that position 
for the duration of their terms as chairmen of the local sections. Section officers 
shall hold office for one year, or until their successors are chosen. 

MID-WEST SECTION 

The first meeting of the season of the Mid- West Section was held on September 
10th at 8 P. M. at the meeting rooms of the Western Society of Engineers, Chicago. 
Mr. Karl Brenkert of the Brenkert Light Projection Company presented a paper 
on "The New Brenkert 80 Motion Picture Projector." The projector was de- 
scribed in detail and demonstrated. 

The meeting was well attended and plans are being made for an interesting 
series of presentations during the winter season. 

ADMISSIONS COMMITTEE 

At a recent meeting of the Admissions Committee at the General Office of the 
Society, the following applicants for membership were admitted to the Associate 
grade : 

BAKER, H. W. BECKMAN, C. 

International Projector Corp., 1333 Bay Ridge Parkway, 

92 Gold Street, Brooklyn, N. Y. 
New York, N. Y. 

432 



SOCIETY ANNOUNCEMENTS 



433 



BERGMAN, L. V. 

732 Eastern Parkway, 

Brooklyn, N. Y. 
BLOEDEL, W. H. 
828 N. Vista St., 

Hollywood, Calif. 
CHAMBERS, I. M. 
629 N. Laurel Ave., 

Los Angeles, Calif. 
CROSS, W. E. 
2918 Pennsylvania Ave., 

Detroit, Mich. 
DEAN, C. E. 

5825 Little Neck Parkway, 
Little Neck, L. I., N. Y. 
DELLAGE, C. J. 
Box 143, 

Eldora, la. 
DUCHARME, M. 
3420 Fullum St., 

Montreal, P. Q., Canada. 
FALCONER, R. H. 
235 Baker Library, 
Hanover, N. H. 
GLASS, P. 

156 West 105th St., 
New York, N. Y. 
Guss, P. S. 

142 East 1st South St., 

Salt Lake City, Utah. 
HOWARD, L. W. 
525 W. Center St., 
Anaheim, Calif. 



KELLNER, C. 
2375 East 16th St., 
Brooklyn, N. Y. 
KERMAN, E. W. 
1447 Cory Drive, 
Dayton, Ohio. 
LEVINE, H. 

13828 78th Drive, 

Kew Gardens, L. I., N. Y. 
PETTUS, J. L. 
4905 East 13th St., 
Indianapolis, Ind. 
PRATER, J. R. 
Congress Theater, 
Palouse, Wash. 
ROGERS, D. C. 

162 West 54th St., 
New York, N. Y. 
SCHNEIDER, A. F. 
640 University St., 
Springfield, Mo. 

SCHOMACKER, M. T. 

2045 Foxhills Drive, 

West Los Angeles, Calif. 
SHUEY, C. W. 
2506 W. 81st St., 

Inglewood, Calif. 
^ SIEVERS, E. S. 

1461 Allison Ave., 

Los Angeles, Calif. 
WADDELL, D. 
164 Broadway, 
Bangor, Maine. 



In addition, the following applicants have been admitted to the Active grade : 



CARLSON, F. E. 

Engineering Department, 
General Electric Company, 
Nela Park, 

Cleveland, Ohio. 

CHONG, J. B. 
1217 Taft Bldg., 
Hollywood, Calif. 



HARSHBARGER, W. J. 
R. D. No. 1, River Road, 

Somerville, N. J. 
HULL, G. F. 
2355 Morris Ave., 

Bronx, N. Y. 
MUNSON, A. L. 
4246 Deyo Ave., 
Congress Park, 111. 



WING, F. M., JR. 
245 West 55th St., 
New York, N. Y. 



Statement of the Ownership, Management, Circulation, Etc., Required by the 

Acts of Congress of August 24, 1912, and March 3, 1933, of Journal of the Society 

of Motion Picture Engineers, published monthly at Easton, Pa., for October 1, 

1940. 

State of New York \ 

County of New York / bv 

Before me, a Notary Public in and for the State and County aforesaid, person- 
ally appeared Sylvan Harris, who, having been duly sworn according to law, 
deposes and says that he is the Editor of the Journal of the Society of Motion 
Picture Engineers and that the following is, to the best of his knowledge and 
belief, a true statement of the ownership, management (and if a daily paper, 
the circulation), etc., of the aforesaid publication for the date shown in the above 
caption, required by the Act of August 24, 1912, as amended by the Act of 
March 3, 1933, embodied in section 537, Postal Laws and Regulations, printed 
on the reverse of this form, to wit: 

1. That the names and addresses of the publisher, editor, managing editor, 
and business managers are: 

Name of Post Office Address 

Publisher, Society of Motion Picture Engineers, Hotel Pennsylvania, New York, 

N.Y. 

Editor, Sylvan Harris, Hotel Pennsylvania, New York, N. Y. 
Managing Editor, Sylvan Harris, Hotel Pennsylvania, New York, N. Y. 
Business Manager, Sylvan Harris, Hotel Pennsylvania, New York, N. Y. 

2. That the owner is: (If owned by a corporation, its name and address 
must be stated and also immediately thereunder the names and addresses of 
stockholders owning or holding one per cent or more of total amount of stock. 
If not owned by a corporation, the names and addresses of the individual owners 
must be given. If owned by a firm, company, or other unincorporated concern, 
its name and address, as well as those of each individual member, must be given). 
Society of Motion Picture Engineers, Hotel Pennsylvania, New York, N. Y. 

E. A. Williford President, 30 East 42nd St., New York, N. Y. 

J. Frank, Jr., Secretary, 356 W. 44th St., New York, N. Y. 

R. O. Strock, Treasurer, 35-11 35th St., Astoria, Long Island, N. Y. 

3. That the known bondholders, mortgagees, and other security holders 
owning or holding 1 per cent or more of total amount of bonds, mortgages, or 
other securities are: (If there are none, o state). 

None. 

4. That the two paragraphs next above, giving the names of the owners, 
stockholders, and security holders, if any, contain not only the list of stockholders 
and security holders as they appear upon the books of the company but also, 
in cases where the stockholder or security holder appears upon the books of the 
company as trustee or in any other fiduciary relation, the name of the person or 
corporation for whom such trustee is acting, is given; also that the said two 
paragraphs contain statements embracing affiant's full knowledge and belief 
as to the circumstances and conditions under which stockholders and security 
holders who do not appear upon the books of the company as trustees, hold stock 
and securities in a capacity other than that of a bona fide owner; and this affiant 
has no reason to believe that any other person, association, or corporation has 
any interest direct or indirect in the said stock, bonds, or other securities than 
as so stated by him. 

5. That the average number of copies of each issue of this publication sold 
or distributed, through the mails or otherwise, to paid subscribers during the 
six months preceding the date shown above is: (This information is required 
from daily publications only). 

SYLVAN HARRIS, Editor, Business-Manager. 

Sworn to and subscribed before me this 21st day of September, 1940. 

(Seal) Wm. J. Miller. 

Notary Public, Clerk's No. 412, New 
York County. Reg. No. 2M 286 
(My commission expires March 30, 1942) 



JOURNAL 

OF THE SOCIETY OF 

MOTION PICTURE ENGINEERS 

Volume XXXV November, 1940 



CONTENTS 

Page 

Commercial Motion Picture Production with 16-Mm Equip- 
ment J. A. MAURER 437 

Advancement in Projection Practice . . . . F. H. RICHARDSON 466 



The Elimination of Hypo from Photographic Images 

J. I. CRABTREE, G. T. EATON, AND L. E. MUEHLER 484 



New Motion Picture Apparatus 

A New Recording Machine Combining Disk Recording and 
Magnetic Recording, with Short Reference to the Present 
Status of Each S. J. BEGUN 507 



Current Literature 522 



Fall Convention at Hollywood, Calif., October 21-25, 1940 

Additional Summaries of Papers 523 



Standards Committee Report 525 



JOURNAL 

OF THE SOCIETY OF 

MOTION PICTURE ENGINEERS 



SYLVAN HARRIS, EDITOR 

Board of Editors 
J. I. CRABTREE, Chairman 

A. N. GOLDSMITH A. C. HARDY T. E. SHEA 

J. G. FRAYNE L. A. JONES G. E. MATTHEWS 

A. C. DOWNES E. W. KELLOGG 



Subscription to non-members, $8.00 per annum ; to members, $5.00 per annum, 
included in their annual membership dues; single copies, $1.00. A discount 
on subscription or single copies of 15 per cent is allowed to accredited agencies. 
Order from the Society of Motion Picture Engineers, Inc., 20th and Northampton 
Sts., Easton, Pa., or Hotel Pennsylvania, New York, N. Y. 
Published monthly at Easton, Pa., by the Society of Motion Picture Engineers. 

Publication Office, 20th & Northampton Sts., Easton, Pa. 
General and Editorial Office, Hotel Pennsylvania, New York, N. Y. 

West Coast Office, Suite 226, Equitable Bldg., Hollywood, Calif. 
Entered as second class matter January 15, 1930, at the Post Office at Easton, 
Pa., under the Act of March 3, 1879. Copyrighted, 1940, by the Society of 
Motion Picture Engineers, Inc. 

Papers appearing in this Journal may be reprinted, abstracted, or abridged 
provided credit is given to the Journal of the Society of Motion Picture Engineers 
and to the author, or authors, of the papers in question. Exact reference as to 
the volume, number, and page of the Journal must be given. The Society is not 
responsible for statements made by authors. 



OFFICERS OF THE SOCIETY 

* President: E. A. WILLIFORD, 30 East 42nd St., New York, N. Y. 

* Past-President: S. K. WOLF, RKO Building, New York, N. Y. 

* Executive Vice-President: N. LEVINSON, Burbank, Calif. 

** Engineering Vice-President: D. E. HYNDMAN, 350 Madison Ave., New York, 
N. Y. 

* Editorial Vice-President: J. I. CRABTREE, Kodak Park, Rochester, N. Y. 

** Financial Vice-President: A. S. DICKINSON, 28 W. 44th St., New York, N. Y. 

* Convention Vice-President: W. C. KUNZMANN, Box 6087, Cleveland, Ohio. 

* Secretary: J. FRANK, JR., 356 W. 44th St., New York, N. Y. 

* Treasurer: R. O. STROCK, 3511 35th St., Astoria, Long Island, N. Y. 

GOVERNORS 

* M. C. BATSEL, Front and Market Sts., Camden, N. J. 

* J. A. DUBRAY, 1801 Larchmont Ave., Chicago, 111. 
** A. N. GOLDSMITH, 580 Fifth Ave., New York, N. Y. 
** H. GRIFFIN, 90 Gold St., New York, N. Y. 

* P. J. LARSEN, 29 S. Munn Ave., East Orange, N. J. 

* L. L. RYDER, 5451 Marathon St., Hollywood, Calif. 

** A. C. HARDY, Massachusetts Institute of Technology, Cambridge, Mass. 

* H. G. TASKER, 5451 Marathon St., Hollywood, Calif. 

* Term expires December 31, 1940. 



j- ti 111 ^.-vjJiiwo .*-/ wv.wnj. u\~i. fXp Xt^xxSi 

** Term expires December 31, 1941, 



COMMERCIAL MOTION PICTURE PRODUCTION WITH 
16-MM EQUIPMENT* 

JOHN A. MAURER** 



Summary. Improvements in film characteristics together with progress in film 
laboratory technic and in 16 -mm sound recording during the past few years have 
made it possible to produce sound motion pictures directly on 16-mm film with both 
picture and sound quality comparable to the results obtained in the past by optical 
reduction from 35-mm negatives, and at considerably reduced cost. This method is 
of special value in the production of training films and other types of industrial and 
educational motion pictures requiring much of the photography to be done away from 
studio facilities. 

This paper discusses the apparatus available for direct 16-mm production, the film 
types that are in use, the film laboratory services that are available, and the methods 
that are used by direct 16-mm producers in the cases where these methods differ from 
those of the 35-mm producer. Particular attention is given to the Kodachrome 
process as used in commercial motion picture production. 



The use of 16-mm prints for the projection of industrial and edu- 
cational motion pictures has today become almost universal. In these 
non-theatrical applications of motion pictures the superior conveni- 
ence and economy of 16-mm equipment made inevitable the dis- 
placement of larger film sizes. At the same time these advantages 
have made possible the employment of films in business and in the 
schools on a much wider scale than would have been possible with 
previously existing films and equipment. 

Production of school and business films directly in the 16-mm size 
is a development that has come much more slowly. Most of these 
subjects are still photographed on 35-mm film even though, as a rule, 
they are intended for projection only in the 16-mm size. 

During the past few years, however, rapid technical progress has 

* Presented at the meeting of the Atlantic Coast Section January 10, 1939; 
revised and re-presented at the 1940 Spring Meeting at Atlantic City, N. J. 
** The Berndt-Maurer Corp., New York, N. Y. 

437 



438 J. A. MAURER [j. s. M. P. E. 

stimulated an already active interest in the possibilities of direct 
16-mm picture photography and sound recording, with the result that 
numerous film subjects have been produced entirely with 16-mm 
equipment. Those who are familiar with the present results of this 
activity believe that direct 16-mm production holds the possibility 
of another considerable extension of the field of usefulness of non- 
theatrical motion pictures. 

A correct appraisal of the value of equipment or methods in any 
field requires a knowledge of the type of service for which they are 
intended. In considering direct 16-mm motion picture production it 
is particularly important to have clearly in mind the proper scope of 
16-mm production activities. It has been pointed out that the two 
factors of convenience and economy are mainly responsible for the 
present wide use of 16-mm films and projectors. In production the 
use of direct 16-mm equipment will be desirable in proportion to the 
extent to which greater convenience and lower cost are obtained with- 
out undue sacrifice of quality. 

Certain types of industrial films, notably sales films designed to 
appeal to large audiences, require elaborate studio facilities and ex- 
pensive acting talent. In the budget of such a film the cost of photog- 
raphy on either 35-mm or 16-mm film is a decidedly minor item. 
Therefore in this field there is nothing to be gained by the use of 
16-mm equipment. In the production of training films, on the other 
hand, most of the photography must be done "on location" in the 
actual manufacturing plant, mine, or laboratory. Here the cost of 
photography, including the costs of film and processing, the time of 
the camera crew, and the cost of any interference with plant produc- 
tion, is the principal cost of the film, and here the savings effected by 
16-mm operation become important. 

Convenience has two aspects, its inherent desirability and its 
effect upon costs. A 35-mm camera adequately equipped even for 
newsreel work is necessarily large enough and heavy enough that it is 
by no means easy to move around with it. A magazine case con- 
taining two or three reels of film loaded and ready for use is all that 
the average man would be interested in carrying for any distance. 
By comparison a 16-mm camera and its supply of film are extremely 
easy to handle. These differences in size and weight make it possible 
to handle 16-mm equipment more rapidly, with the result that loca- 
tion filming can be accomplished in a considerably shorter time than 
is required when using 35-mm cameras. 



Nov., 1940] 



COMMERCIAL 16-MM PRODUCTION 



439 



A similar situation exists when a sales film is being produced to 
appeal to a small or highly selected audience on the basis of "the 
reason why." This type of sales film depends for its effectiveness on 
the force and timeliness of the ideas presented rather than on elabo- 
rateness of treatment, and can generally be produced more quickly, 
more conveniently, and less expensively by the direct 16-mm method. 

The obvious aspect of the economy of working in 16-mm, that is, 
the lower cost of film and processing, is usually the least important. 




FIG. 1. 



Direct 100-diameter enlargement from 16-mm negative on Cine 
Kodak Safety Panchromatic Negative Film. 



It is true that the ratio of film cost between 35-mm and 16-mm is of 
the order of 3 to 1. Where pictures are taken for record or study 
purposes, this difference frequently means that a project can be 
carried out with 16-mm equipment, whereas it would be prohibitively 
costly in 35-mm. But in general the cost of film itself is unimportant 
in comparison with the savings that result from using 16-mm equip- 
ment because of its greater mobility, its ability to turn out more work 
in a given time, and lower handling and transportation costs. 

The safety of the 16-mm film itself is another important advantage 
when production work is being carried on in school or factory. The 



440 J. A. MAURER [j. s. M. P. E. 

fire-proof storage vaults and projection rooms required for working 
with 35-mm film are not only expensive, they are also inconvenient, 
and in many cases impossible to install. This fact alone permits 
many institutions to engage in 16-mm film production when 35-mm 
production would be out of the question. 

It should be recognized that in the past there have been technical 
reasons for preferring to photograph in the 35-mm size that have 
outweighed considerations of cost and convenience. With the ma- 




FIG. l(a). Enlargement of entire frame corresponding to Figs. 1, 3, etc., 
showing the portion enlarged to 100 diameters in these figures. 

terials available ten years ago, and even five years ago, it was im- 
possible to turn out 16-mm prints from 16-mm originals with picture 
quality good enough to be satisfactory in comparison with pictures 
photographed on 35-mm film and optically reduced. Excellent pic- 
ture quality was obtained, of course, on original reversal films. Proc- 
esses of duplication, however, left much to be desired. Direct 16-mm 
negatives gave images that were far too grainy to be acceptable. In 
addition, the physical properties of the acetate film base introduced 
limitations which will be discussed later in this paper. Furthermore, 
the equipment and film laboratory services existing in the 16-mm 



Nov., 1940] COMMERCIAL 16-MM PRODUCTION 441 

field during this period were not adequate for the needs of commer- 
cial film producers. 

In view of the fact that the removal of these limitations having to 
do with the film is the principal reason for the present increase of 
16-mm activity, this is probably the best point at which to begin a 
general study of the methods and tools that are being used by direct 
16-mm producers. 

It is a matter of general knowledge that an astonishing improve- 
ment in film emulsion characteristics has taken place during the past 




FIG. 2. 100-diameter enlargement of small portion of sensitometric strip 
on Eastman Positive film (Type 5301). 

three years. Increases of speed have been well advertised. The 
improvement in grain structure that has been obtained in materials 
of less sensational speed has also been well advertised, but has perhaps 
received less general attention. This reduction in graininess has com- 
pletely changed the situation that formerly existed when comparing 
prints from 16-mm negatives with those made by optical reduction 
from 35-mm negatives. 

In the past, most of us have been in the habit of thinking of stand- 
ard positive film as a fine-grained material. It will possibly surprise 
many workers in the industry to learn that today high-speed negative 



442 



J. A. MAURER 



[J. S. M. P. E. 



films are available that are capable of yielding images actually finer 
in grain structure than those of standard positive film. 

Figs. 1 to 4 show some of these graininess relationships. Fig. 1 is a 
direct 100-diameter enlargement of a small portion of a 16-mm nega- 
tive made on Cine* Kodak Safety Negative Film of the type being 
marketed at the present time. (This film appears to have practically 
the same emulsion as Background X 35-mm film.) Fig. 2 is another 
100-diameter enlargement showing the grain structure of a strip of 




FIG. 3. 






100-diameter enlargement of print from negative of Fig. 1 on 
Eastman Positive film (Type 5301}. 



positive film exposed and developed to a density matching the face 
tones in Fig. 1. Fig. 3 shows a contact print from the negative shown 
in Fig. 1 on film of the type shown in Fig. 2. 

By comparing Figs. 1, 2, and 3 it may readily be seen that the 
grain of the positive printing stock has contributed at least as much 
to the appearance of graininess in the print as the grain of the nega- 
tive. 

In optical reduction printing the grain structure of the negative is 
reduced approximately 2 J /2 diameters, and also it is usually diffused 
because of lack of perfect definition in the lens system of the printer 



Nov., 1940] 



COMMERCIAL 16-MM PRODUCTION 



443 



to such an extent as to be practically lost. In an optical reduction 
print, therefore, almost all of the effect of graininess is due to the 
positive stock. 

Fig. 4 is a 100-diameter enlargement of a small portion of an op- 
tical reduction print, chosen because it contains flesh tones closely 
matching those of Fig. 3 in density. It will be noted that the graini- 
ness of the image in Fig. 4 is practically the same as that in Fig. 3. 
This demonstrates the relative unimportance of the 16-mm negative 




FIG. 4. 



100-diameter enlargement of optical reduction print on Eastman 
Positive film (Type 5502). 



as a source of grain, and shows why it is now possible to obtain con- 
tact prints from 16-mm negative that compare well with prints made 
by optical reduction from 35-mm negatives. 

The negative-positive process has been used as the example to show 
the present improved state of film emulsion characteristics because it 
is the most nearly comparable to the usual 35-mm procedure, and 
because, in the past, it has been the least satisfactory of all ways of 
obtaining 16-mm picture prints. Other procedures which the writer 
believes to be more generally desirable will be discussed later in this 
paper. 



444 J. A. MAURER [j. s. M. P. E. 

A wide variety of camera types is today available to the 16-mm 
producer. These may be classified roughly as (1) spring-driven ama- 
teur cameras, (2) motor-driven and otherwise specially equipped 
amateur cameras, and (3) cameras primarily designed for professional 
use. 

Cameras of the first class are by no means useless in commercial 
work. Used intelligently, all those of reputable make are capable of 
meeting all normal requirements as to steadiness and sharpness of 




FIG. 4(a). An enlargement of the pianist's left hand is shown in Fig. 4. 



pictures. Since their motive power is self-contained, and they require 
for an average day's operation no more film than can be carried in the 
cameraman's coat pockets, they lend themselves especially well to 
the filming of industrial plant operations, where it is generally impor- 
tant to get the picture without interfering with production. Among 
the most desirable types are the magazine-loading cameras, which 
offer the extreme in small size and convenience. 

The most serious limitation of the typical amateur camera is the 
inaccuracy of its finder. These finders are generally adjusted to be 
correct for a distance of fifteen feet. At other object distances errors 



Nov., 1940] 



COMMERCIAL 16-MM PRODUCTION 



445 



of parallax enter which are especially troublesome when lenses of 
longer focal length than the customary one inch are in use. In the 
Cin Kodak Special this limitation is largely removed by the pro- 
vision of a reflex focusing mechanism which permits viewing the 
actual image of the lens that is in taking position. It is probably for 
this reason that the Cin6 Kodak Special has been more widely used 
for commercial motion picture production than any other 16-mm 
camera. 

A good example of the second class of camera is the Bell & Howell 
Filmo equipped with synchronous motor drive and external 400-foot 
film magazine. These attachments make the camera usable for syn- 
chronous picture and sound-recording work, although it is usually 




FIG. 5. Horizontal sectional view of part of Berndt-Maurer "Sound-Pro" 
camera, showing method of focusing on ground glass. 

necessary to enclose the entire mechanism in a "blimp" in order to 
make it quiet enough for operation near a microphone. Motor 
drives, both synchronous and non -synchronous, are also available 
for the Cine* Kodak Special. This camera likewise requires some 
form of sound-insulating enclosure when it is to be used near a micro- 
phone. 

Among the numerous accessories that are available for use with the 
Cine Kodak Special, the auxiliary finder, adjustable for parallax, and 
the focusing microscope attachment deserve special mention. Be- 
cause these attachments increase the accuracy with which the camera 
can be used, they are generally employed by cameramen doing com- 
mercial work with the "Special." 

Aside from the fundamental ability to produce steady pictures, 
the most important requirements of a camera for professional work 



446 J. A. MAURER [J. S. M. P. E. 

are accurate finding and focusing. All the cameras that have found 
extensive use in 16-mm commercial production have provision in 
some form for focusing on ground glass. In the Bell & Howell Filmo 
this is accomplished by rotating the lens turret so as to bring the lens 
in front of a ground-glass which is viewed through a magnifying lens 
and reflecting prism. In order to focus the Cind Kodak Special a 
first-surface mirror is introduced between the lens and the shutter, 
thus reflecting the image to a ground-glass screen viewed either di- 
rectly through a magnifying lens or indirectly through the micro- 
scope attachment referred to above. This system has the important 
advantage that it avoids moving the lens from its operating position. 
In the Magazine Cin Kodak a microscope unit can be substituted 
for the magazine of film, thus making possible very accurate focusing 
and composition of the subject in the picture area. 

In the Berndt-Maurer "Sound- Pro" camera, which is designed 
primarily for professional use, these provisions for accurate focusing 
and picture composition are carried out with maximum accuracy. 
The focusing system is shown in Fig. 5 and Fig. 6. Picture-gate and 
pull-down mechanism are mounted on a dovetailed slide which also 
carries a separate focusing aperture covered with fine ground glass. 
For focusing, this slide is moved laterally so as to bring the focusing 
aperture to the lens axis. In this position the ground glass is viewed 
through a microscope magnifying eight diameters. 

The regular finder of the Sound-Pro camera shown in Fig. 7 is of the 
inverting prism type, the image being formed on a ground glass, 
accurately framed. The image is right side up and correct as to left 
and right. The finder is adjustable for parallax, and contains internal 
adjusting features by which the field it shows can be made to corre- 
spond accurately to the actual field of the taking lens, even though 
the latter is not perfectly centered in its mount, a not uncommon 
condition. 

Since most industrial and educational pictures today are produced 
with sound, quiet operation is a necessity in a professional 16-mm 
camera. Since this was not an objective in the design of the amateur 
types, it is necessary to "blimp" them when they are to be used for 
pictures synchronized with sound. It may be doubted whether the 
degree of silence in operation that is required for synchronous studio 
operation can be obtained without extreme mechanical precision in 
the construction of the camera. This necessarily makes the truly 
professional instrument much more costly than the amateur types. 



Nov., 1940] 



COMMERCIAL 16-MM PRODUCTION 



447 



Fortunately for the convenience of the producer, the majority of in- 
dustrial and educational motion pictures are most effective when the 
sound takes the form of spoken commentary with background music 
or sound effects. This type of sound accompaniment is, of course, 
scored after the picture has been completely photographed and edited. 
Under these conditions a quiet running camera is not needed. 

Although it has now become an easy matter to introduce fades and 
dissolves in the film laboratory on 16-mm film, the professional cam- 




FIG. 6. View of "Sound-Pro" camera with door open, showing gate shifted 
into focusing position. 

eraman naturally wishes to have his camera equipped to produce 
these effects directly. Both the Cine Kodak Special and the Berndt- 
Maurer Sound-Pro cameras are so equipped. In the latter case 
both automatic and manual shutter controls are provided. 

A minor difficulty that sometimes causes annoyance when working 
with 16-mm cameras is a variation in position of the frame line with 
different batches of film stock. This can occur in any camera in which 
there is a distance of several frames of film between the picture aper- 
ture and the terminal position of the pull-down claw. The cause is 
shrinkage of the film stock with age, which produces the frame-line 



448 J. A. MAURER [j. s. M. P. E. 

displacement in the manner illustrated in Fig. 8. The basic remedy 
consists in designing cameras with the pull-down mechanism as close 
as possible to the picture aperture. A practical remedy that can be 
applied by the cameraman is to avoid the use on the same produc- 
tion of film several months old and film that has just been purchased. 
Film manufacturers could help this situation materially by sealing 




FIG. 7. "Sound-Pro" camera with door closed, showing 
finder and focusing microscope. 



their film containers so as to prevent the escape of moisture and con- 
sequent shrinkage of the film with age. This is usually not done in 
the case of the reversal films now on the market. 

Films for 16-mm picture photography naturally fall into three 
classifications, (1) black- and-white reversal films, (2) black-and-white 
negative films, and (3) color-films. These, in turn, lead to a con- 
siderable diversity of possibilities in the production of copies for dis- 
tribution. Most of the possible methods have been tried out thor- 



Nov., 1940] 



COMMERCIAL 16-MM PRODUCTION 



449 



oughly in practice, and can be appraised with considerable definite- 
ness. 

Well photographed original reversal gives the best picture quality 
that can at present be obtained on 16-mm film. This quality can be 



CAMERA 
APERTURE 



D 



I CLAW 



CAMERA 
APERTURE 



a 



a 



UNSHRUNK FILM 



FILM SHRUNK 



FIG. 8. Diagram drawn accurately to scale, showing how 
film shrinkage can produce frame-line displacement in im- 
properly designed cameras and printers. 



approached in carefully made prints from either 35-mm or 16-mm 
negatives provided fine-grain film is used for the print, but it can 
not be equalled by any process known to the writer. Reversal images 
are characterized by fineness of grain, excellent sharpness of image, 



450 J. A. MAURER [J. s. M. P. E. 

and a clear, sparkling quality that is difficult to match by other 
processes. 

Unfortunately for the professional who is attempting to use re- 
versal films for the first time, most of them require a lighting technic 
quite different from that which gives the best results with negative 
films. Reversal films have been developed to satisfy the taste of 
amateur users, who, as is well known, generally like "brilliant," that 
is to say, high contrast, results better than the delicate tone gradation 
for which the professional is likely to strive. 

That high contrast is not a necessary property of reversal films 
is indicated by the fact that one "supersensitive" film which was on 
the market for several years was of low contrast, and gave excellent 
long-scale reproduction. This film was withdrawn from the market 
when it became possible to produce films of both higher speed and 
higher contrast. 

Of the reversal films now on the market the most rapid available, 
Agfa SSS Superpan and Eastman Super XX Panchromatic, give the 
softest tone rendition. In spite of their remarkably high speed, both 
these films give excellent image quality and are to be recommended 
as the most generally satisfactory for commercial work. 

Because of the somewhat high contrast of even these ultra-rapid 
reversal films, the professional photographer who is using them for 
the first time should light his subject rather more flatly than he is 
accustomed to doing. This does not mean that brilliant backlighting 
is to be avoided, for the reversal process reproduces this type of light- 
ing unusually well. What is important is to maintain a high level of 
general illumination relative to the light used for "modeling," so as 
to avoid excessively dark, empty shadows in the final result. On 
the other hand, effects of striking contrast, with jet black shadows, 
when desired, can be obtained better on reversal film than on any 
other medium. 

Copies of pictures photographed on reversal film are being made 
commercially by two processes: (1) reversal duplication, and (2) 
positive printing from an intermediate negative made on fine-grain 
duplicating film. 

Until the appearance of suitable fine-grain film for negative mak- 
ing, reversal duplication was the only satisfactory means of producing 
copies from reversal originals. The process gives a fine-grain image 
and good tone rendition, but suffers from two faults. The more seri- 
ous of these is a tendency to produce a white line, sometimes amount- 



Nov., 1940] 



COMMERCIAL 16-MM PRODUCTION 



451 



ing to a conspicuous halo, around any dark object which stands 
against a medium gray background. This is a form of the well known 
"Eberhardt effect." The second defect is a lack of volume in the 
reproduction of sound-tracks printed on reversal duplicating film. 
The nature of the reversal process is such that it is very difficult to 
obtain complete transparency even where the exposure has been 
very high. This limits the modulation range of both variable-area 
and variable-density sound-tracks to such a degree that the level ob- 




FIG. 9. 100-diameter enlargement of picture on original reversal film. 



tained in reproduction is from six to twelve, or in some cases as much 
as fifteen, decibels lower than is obtained with positive prints from 
sound-track negatives. This loss of reproduction level is not great 
enough to make the results unusable, but it does have an undesirable 
effect on the ratio of signal to background noise obtained with the 
average 16-mm sound projector. 

Because of the above-mentioned faults of the reversal duplicating 
method, and because it is more costly than the intermediate negative 
and positive print method, the latter is to be preferred for practically 
all commercial purposes. 



452 J. A. MAURER [j. S. M. P. E. 

Figs. 9, 10, and 11 will give some idea of the quality that is being 
obtained commercially in the duplication of reversal originals by 
means of fine-grain duplicating negative and positive printing stocks. 
Fig. 9 is a 100-diameter enlargement from an original reversal image 
of the same subject shown in Figs. 1, 2, and 3. Fig. 10 is a similar 
enlargement from a negative printed from this reversal original on 
Eastman type 5203 panchromatic duplicating stock. Fig. 11 shows 





FIG. 10. Direct 100-diameter enlargement from negative on Eastman 
type 5203 fine-grain panchromatic duplicating stock, printed from the re- 
versal original shown in Fig. 9. 



a print from the negative of Fig. 10 on DuPont fine-grain positive 
stock. 

A comparison of Fig. 11 with Fig. 4 shows that the reversal-inter- 
mediate-negative-positive-print process leads to results that are su- 
perior to what might be termed standard optical-reduction prints 
from the standpoint of fineness of grain, and at least equal to them 
in sharpness of image. Valid comparisons of tone rendition are prac- 
tically impossible to carry through the process of reproduction by 
photoengraving. It is fair to state, however, that the tone rendition 
of prints obtained in regular commercial practice by this process ap- 



Nov., 1940] 



COMMERCIAL 16-MM PRODUCTION 



453 



proximates that of the reversal originals as closely as is usual in 35-mm 
duplicating practice. When the original has been slightly under or 
overexposed, or is either too flat or too contrasty, it is usually possible 
to make a print from the intermediate negative that will appear much 
better on the screen than the original itself. 

The reversal-intermediate negative procedure for producing prints 
of 16-mm subjects has several advantages that are not immediately 
obvious. It safeguards the production in the same manner as the 




FIG. 11. 100-diameter enlargement of print from negative of Fig. 10 on 
DuPont type 5757 fine-grain positive stock. 

making of a "lavender" print in 35-mm practice, since the original, 
after editing, is run through the printer only once to make the fine- 
grain negative. A practically unlimited number of prints of a sub- 
ject is possible, since new fine-grain negatives can always be printed 
from the original. It combines the fine-grain image advantage of re- 
versal photography with the ability to control contrast provided by 
the negative-positive process. Optical printing effects, such as fades, 
dissolves, and wipes, are produced directly in the printing of the 
fine-grain negative, and therefore are not liable to the abrupt changes 
in picture density or quality, or both, often seen in 35-mm work where 



454 



J. A. MAURER 



[J. S. M. P. E. 



short sections of original negative before and after the effect have 
been replaced by the duplicate negative carrying the effect. This is 
one of the major advantages of working from a positive original. 

There is a more important reason than all the above, however, for 
preferring to use reversal film for 16-mm commercial motion picture 
photography. This is the vastly greater ease and certainty with 
which reversal positives can be edited, as compared with negative 
film. Because of the small size of a 16-mm negative, every scratch, 




FIG. 12. Direct 100-diameter enlargement from 16-mm negative on 
Agfa Superpan Supreme, showing grain structure representative of modern 
extremely rapid films. 

and every particle of dirt, impressed on the film during editing, will 
be objectionably apparent as a white mark on the screen when the 
positive print is projected. Similar defects in a positive original pro- 
duce black markings on the final print, and these as a rule are im- 
possible to see on the screen. Splices in a reversal original are seldom 
noticeable when the print is projected; splices in a 16-mm negative 
must be made with extreme care if they are not to be conspicuous on 
the screen. The net effect is that it is relatively easy even for an 
untrained person to edit a reversal original so as to produce a clean 
effect when the final print is projected, whereas the editing of a 16- 



Nov., 1940] COMMERCIAL 16-MM PRODUCTION 455 

mm negative requires expert handling under clean conditions if the 
final result is to be free from mechanical blemishes appearing as white 
marks or flashes on the screen. This difficulty does not appear in the 
case of the fine-grain intermediate negative printed from the reversal 
original because this negative (usually) contains no splices and re- 
ceives no handling other than is incidental to printing. In the hands 
of well trained film laboratory personnel such a negative will yield at 
least fifty prints before becoming noticeably abraded. 

In spite of the difficulty of editing 16-mm negatives, a considerable 
number of producers have preferred to work by the negative-positive 
process, partly because it reduces film costs to a minimum, and partly 
because as individuals they were familiar with the photographic tech- 
nic of negative films and preferred not to attempt the unfamiliar 
technic of reversal. The results have proved that in spite of the 
difficulties pointed out above, 16-mm negative-positive is today a 
useful process. 

There are at the present time (August, 1940) four types of negative 
film available in the 16-mm size. These are Cine Kodak Safety Nega- 
tive Film (Panchromatic), Cine* Kodak Super XX Negative Film, 
Agfa Superpan Supreme, and DuPont Superior Panchromatic. The 
first of these apparently corresponds to Background X 35-mm film; 
the others are similar in properties to the 35-mm negative films of the 
same name. 

The graininess characteristics of the slowest of these films (Cin 
Kodak Safety Negative Film) have already been indicated in the 100- 
diameter enlargements, Fig. 1 and Fig. 3. Figs. 12 and Fig. 13 show 
the graininess characteristics of Agfa Superpan Supreme, which is 
representative of the three faster films. While the reader will notice 
that the graininess of this negative and print is considerably greater 
than that shown in Figs. 1, 3, 9, 10, and 11, it should be pointed out 
that in actual practice the degree of graininess shown in Fig. 13 
has not been found objectionable. It is probable that more 16-mm 
commercial productions have been photographed on this film than 
on any other of the negative types, and of these several have had 
wide distribution. (One of the pictures projected at the Atlantic 
City convention in April as an example of 16-mm negative-positive 
work was a commercial production made on Agfa Superpan 
Supreme.) 

For best results these 16-mm negative films require fine-grain 
processing. The DuPont Superior film has for several years been 



456 



J. A. MAURER 



[J. S. M. P. E. 



processed by the manufacturer in a paraphenylene-diamine developer. 
At the Precision Film Laboratories, in New York City, where the 
test-films used for the illustrations in this paper were processed, a 
different type of fine-grain developer, suitable for use in machine de- 
velopment, has been evolved. The results shown in the enlargements 
are, therefore, not typical of what is obtained with rack-and-tank 
processing in conventional developers. 




FIG. 13. 



100-diameter enlargement of print of negative shown in Fig. 12 on 
Eastman Positive film (type 5301). 



It has already been pointed out that the conventional types of 16- 
mm positive printing stock, such as Agfa type 220, DuPont type 600, 
and Eastman type 5501, contribute materially to the graininess of 
either 16-mm contact prints or optical reduction prints from 35-mm 
negatives. Therefore the introduction of a fine-grain positive print- 
ing stock, DuPont type 3737 (corresponding to the 35-mm type 
222), was of unusual significance to the 16-mm field. The quality of 
prints obtained on this stock from the fine-grain intermediate nega- 
tives made from reversal originals has already been indicated by 
Fig. 11. Fig. 14 shows the effect of printing from the negative of Fig. 



Nov., 1940] 



COMMERCIAL 16-MM PRODUCTION 



457 



1 on DuPont type 3737. This print is only a little more grainy than 
the print of Fig. 11, and considerably less grainy than the conven- 
tional optical reduction print of Fig. 4. The improvement in screen 
quality that is obtained by using this fine-grain positive printing stock 
is readily apparent to the critical eye, and is the more worth while be- 
cause a similar improvement in sound-track quality is obtained at the 
same time. 




FIG. 14. 



100-diameter enlargement of print of negative shown in Fig. 1 on 
DuPont type 5757 fine-grain positive film. 



The inherent difficulty of editing 16-mm negatives has already been 
mentioned, but the importance of this point is such that it can hardly 
be emphasized too strongly. The editing of a production photo- 
graphed on 16-mm negative film is the step which, more than any 
other, decides whether or not the final result will be a source of satis- 
faction to those responsible. 

As has been proved by numerous commercial examples, excellent 
results can be obtained in prints from 16-mm negatives. If, then, the 
editing is handled as is customary in cutting 35-mm theatrical pro- 
ductions, that is to say, if the picture is first edited by means of work 



458 J. A. MAURER [J. S. M. P. E. 

prints and the negative is then matched to the edited work print by 
a careful worker, in a room free from dust, with a minimum of han- 
dling, and that only with clean gloves on the hands, the final prints 
may be expected to be clean and free from blemishes. Any scratches, 
fingerprints, or cinch marks on the 16-mm negative will naturally 
appear on the screen on a larger scale than they would if they were 
on a 35-mm negative, but this is somewhat offset by the fact that 
scratches on the negative print with much lower contrast by contact 
than when printed on an optical reduction printer. 

But while the above is a fair statement of the case, it has happened 
several times in the writer's experience that the film editing of an 
otherwise well handled production was entrusted to an inexperienced 
person, with the result that the negative was almost completely 
ruined. Too frequent unwinding and rewinding of small rolls of nega- 
tive, especially in a dusty room, inevitably produce blemishes that 
can not be removed by any amount of cleaning and polishing. Usually 
all that is needed to avoid such excessive handling of negatives is a 
good system of keeping records of the contents of each roll of film. 

The two preceding paragraphs amount to saying that the careful 
worker who knows the precautions necessary in handling negatives 
will have no difficulty in editing 16-mm negative film. But the inex- 
perienced should stick to reversal, which will tolerate much rougher 
handling without showing bad effects on the screen. 

Even in the case of reversal, a work print should be used for the 
editing of any production on which much effort has been expended. 
Such a work print may be made by reversal duplication or, less 
expensively, it may take the form of a negative printed on ordinary 
"positive" stock, or of a positive printed from such a negative. No 
particular care need be required of the laboratory in printing such 
work negatives or work prints, since the object is only to obtain a 
recognizable copy of the original for editing purposes. 

One of the most important of the factors that have led to the pres- 
ent increase of activity in direct 16-mm motion picture production 
has been the availability of the Kodachrome process. This, with the 
perfecting of a satisfactory duplicating procedure, has brought ad- 
vertising and scientific films in color within the means of the average 
business firm, school, or college. A large percentage of direct 16- 
mm productions are today being photographed in color. 

A better description of the technic of commercial production in 
Kodachrome can be given after certain matters pertaining to 16-mm 



Nov., 1940] COMMERCIAL 16-MM PRODUCTION 459 

film laboratory technic and 16-mm sound-recording practice have 
been pointed out. Therefore this topic, which logically belongs here 
in our discussion, will be deferred to the end of the paper. 

It is desirable to note at this point, however, that Kodachrome 
lends itself well to the production of pictures that are to be dis- 
tributed both in black and white and in color. The fine-grain nega- 
tive duplicating stock referred to above, being panchromatic, pro- 
duces, from Kodachrome, negatives having pleasing monochrome 
color rendition and generally satisfactory gradation. Kodachrome, 
being a reversal process, has very fine grain. As a consequence black- 
and-white prints from fine-grain negatives made from Kodachrome 
have the same characteristics as those resulting from black-and-white 
reversal originals. In fact, scenes taken on Kodachrome may be 
edited into a picture taken mostly on black-and-white reversal film, 
and these scenes will not differ noticeably from the others in the final 
print made from the fine-grain negative. This is often a decided 
convenience to the film editor. 

A factor which has necessarily retarded the development of the 
direct 16-mm production field has been the lack of suitable printing 
equipment in film laboratories. This condition still exists in many 
parts of the country, making it necessary for those to whom quality 
is important to send their work to laboratories specializing in 16-mm 
processing. 

It has generally been recognized in the motion picture industry 
that picture printers operating on the step-by-step principle give 
results superior to those of continuous printers. Nevertheless prac- 
tically all 35-mm release printing is successfully handled by con- 
tinuous printers. This fact has led to the construction and use of 16- 
mm continuous printers, which have in general produced less de- 
sirable results. In any continuous hollow-sprocket type of printer 
there is a certain amount of slippage between the negative and the 
positive stock except in the rare case when the negative shrinkage 
is exactly the amount for which the printer sprocket was designed. 
The amount of this slippage is proportional to the distance between 
adjacent sprocket-holes and to the range of shrinkage of the film base. 
In the case of 16-mm films, these values are such that the slippage 
may amount to as much as 0.0015 inch during the passage of the film 
in front of the printing aperture. This is enough seriously to impair 
the sharpness of the image. 

On the basis of the reasoning stated above, the writer is convinced 



460 J. A. MAURER [j. s. M. p. E. 

that for the highest quality of 16-mm contact printing it is necessary 
to use step printers, preferably with pilot-pin registration of the films. 

In some of the step-printing machines that are on the market and in 
practical use, we encounter the same cause of frame-line variation 
that was discussed in connection with Fig. 6. If there is a distance 
of several frames between the pull-down and the printing aperture, 
and if the film being printed consists of sections of different ages and 
therefore of different degrees of shrinkage, the frame line of the nega- 
tive will shift from section to section relatively to the frame line of 
the printer, sometimes greatly to the detriment of the appearance on 
the screen. As a result of his experience the writer is convinced that 
for generally satisfactory performance two frames is the maximum 
distance that ought to exist between the bottom of the aperture and 
the pull-down claw in either a camera or a printer. 

The seriousness of this frame-line difficulty was formerly much 
greater than it is at the present time. During the past few years con- 
siderable improvement in 16-mm film shrinkage characteristics has 
taken place. This is one of the aspects of the general improvement in 
films which has contributed to make direct 16-mm picture production 
a practical commercial undertaking. 

While industry still finds a number of uses, such as motion study, 
for the silent motion picture, the distribution of sound projectors 
has now become so wide that most industrial and educational pic- 
tures are produced with sound. Without direct 16-mm sound-re- 
cording equipment, direct 16-mm production would be out of the 
question. 

At the present time both single-system, or newsreel type, and 
double-system 16-mm sound-recording equipment are available. 
Because of the limitations which the single-system procedure im- 
poses in editing, however, this type of equipment is little used by com- 
mercial film producers and will not be discussed here. 

Sixteen-mm sound recorders for double-system operation have been 
built by the Berndt-Maurer Corp. since the year 1935. Fig. 15 shows 
the machine at present manufactured. Sixteen-mm recorders are 
also manufactured in the United States by the Herman A. DeVry 
Corp., the Canaday Sound Equipment Co., and by the C. R. Skinner 
Mfg. Co. A variable-density recorder for 16-mm film developed by 
Electrical Research Products, Inc., was described before this Society 
at the Detroit Convention in the fall of 1938. 1 The results obtained 
with the Berndt-Maurer recorder, which uses the variable-area sys- 



Nov., 1940] COMMERCIAL 16-MM PRODUCTION 461 

tern, were described and demonstrated by the writer at the Holly- 
wood Convention of the Society in April, 1939. 2 

Until about the end of the year 1938, practically all 16-mm sound 
recording was done on the standard positive printing stocks (Agfa 
type 220, DuPont type 600, Eastman type 5301). Since that time 
two stocks specifically intended for sound recording have been avail- 
able. These are DuPont type 601 and Eastman 5359. Still more 
recently a yellow-dyed film, Agfa type 250, has become available. 




FIG. 15. Berndt-Maurer 16-mm sound recorder. 

These newer films, when used in combination with filters to exclude 
the blue-green range from the recording light-beam, make possible a 
standard of sound quality on direct 16-mm recordings that is far 
superior to that commonly obtained in sound-tracks optically re- 
duced from 35-mm negatives. The last-mentioned stock is of ex- 
ceptionally high resolving power. When sound negatives are re- 
corded on this stock and printed on the fine-grain positive (DuPont 
type 3737), both the frequency range and freedom from distortion 
customarily obtained with 35-mm film can be equalled on 16-mm 
prints. 



462 J. A. MAURER [j. s. M. P. E. 

In 16-mm sound recording, as in 16-mm picture photography, the 
quality of the result is principally determined by the processing and 
printing of the films. Accurate control of density and gamma in de- 
velopment, and printing on high-quality equipment are expected 
as a matter of course in 35-mm processing. Until the advent of film 
laboratories specializing in 16-mm processing it was difficult to ob- 
tain similarly careful handling of 16-mm sound-tracks. Today pro- 
ducers are aware that results of high quality are possible in 16-mm, 
and this realization has resulted in their demanding, and getting, a 
higher standard of work from the entire trade. 

It has been stated above that the conventional hollow-sprocket 
type of continuous printer is not suitable for producing the best 
quality of 16-mm picture prints. It is entirely unsuitable for 16-mm 
sound printing. Either a non-slip printer or an optical one-to-one 
ratio sound-printer so designed as to overcome the effects of shrinkage 
is a necessity. In the writer's experience the optical sound-printer is 
the best of all types. 

The editing of 16-mm sound and picture films presents no prob- 
lems that were not solved long ago in 35-mm practice. The conven- 
tional "synchronizer," consisting of two sprockets attached to the 
same shaft (and usually coupled to a footage meter) serves most pur- 
poses, since numerous retakes of a scene are not common in 16-mm 
production. When scenes involving synchronized sound and picture 
are taken, the clap-stick method of obtaining start marks is generally 
used. This makes it unnecessary to employ a Moviola. A 16-mm 
Moviola is available, however. 

The majority of 16-mm industrial and educational productions re- 
quire "off-stage voice," or commentary, rather than synchronized 
sound. For scoring such sound to match previously edited pictures, 
it is necessary to have a projector operating exactly at synchronous 
speed. This is usually accomplished by coupling the shutter shaft of 
the projector by a flexible shaft to a suitably geared synchronous 
motor. It is immaterial whether or not this motor actually furnishes 
the power to drive the projector so long as it is large enough to control 
the speed. When the picture is projected at synchronous speed, the 
announcer, if he rehearses a sufficient number of times, can readily 
give a performance that requires little or no editing to match it to 
the picture. 

With improved quality in 16-mm recording, it was inevitable that 
there should arise a demand for re-recording equipment. The film 



Nov., 1940] COMMERCIAL 16-MM PRODUCTION 463 

phonograph shown in Fig. 16 was developed by the Berndt-Maurer 
Corp. to meet this need. The machine uses essentially the same 
film-driving mechanism as the recorder, with minor modifications 
to make it suitable for the different shrinkage range encountered when 
running prints instead of raw-film stock. The optical system used to 
scan the sound-track delivers a light-beam 0.0005 inch wide. This 
makes the scanning loss at a given frequency almost exactly the same 




FIG. 16. Berndt-Maurer film phonograph, for rerecording from 16-mm 

sound-tracks. 

as the loss in standard 35-mm reproducing equipment. The steadi- 
ness of film motion is such that re-recorded music betrays no audible 
speed variations. At least one active 16-mm producer is at present 
re-recording the sound for his entire product, using two of these ma- 
chines to carry edited speech and background music (or sound effect) 
tracks. 

The use of 16-mm Kodachrome for industrial motion pictures has 
assumed such importance during the past year that the topic deserves 
separate treatment in order that all the important facts may be as- 
sembled together. 



464 J. A. MAURER [j. s. M. p. E. 

Kodachrome picture duplicates are printed on Type A Koda- 
chrome, using an assembly of special light-filters in combination with 
a light-source of accurately controlled color- temperature. These 
films receive a special type of processing which results in a different 
overall contrast and a different color balance from that obtained in 
the standard processing used for original camera exposures. The 
colors of the original film are reproduced to an excellent approxima- 
tion. 

In work on Kodachrome duplication at the Precision Film Labora- 
tories it has been found possible to a considerable extent to correct 
variations of density among different scenes in an original film, and 
in many cases to correct overall departures from proper color balance. 
Nevertheless it should be stated emphatically that the best way to 
be sure of obtaining a good Kodachrome print is to make sure that 
all scenes included in the original edited film are correctly exposed 
and photographed under light of normal color balance. 

Sound-tracks for printing on Kodachrome are either printed to ob- 
tain good-quality positive prints or are recorded as "direct positives" 
on the yellow-dyed Agfa recording stock (Type 250}. This stock is 
uniquely suitable for the recording of direct positives because it is 
capable of yielding an image of high density with very little "enve- 
lope" distortion. 

Kodachrome itself appears to introduce relatively little distortion ; 
therefore the positive sound-track used for printing should be one 
that reproduces well on a projector or film phonograph. It should be 
of density 1.3 or higher for best results. 

When Kodachrome duplication was a new process the sound 
quality obtained was extremely disappointing, being low in volume 
and high in background noise. These defects have been overcome by 
a process which permits leaving a silver image in the sound-track edge 
of the film in addition to the dye image. Sound-tracks produced in 
this way are only eight to ten decibels lower in level than good black- 
and-white sound-tracks, and are low in background noise. There is 
a definite loss of high-frequency response, but this is not great enough 
to be objectionable when the original sound-track is of good quality. 

Optical printing can be done with Kodachrome, but the tendency 
for slight surface irregularities on the original to appear as blemishes 
in the print (because of their effect in scattering light) is such that 
this method of printing should generally be avoided. 

In general conclusion it may fairly be said that the equipment, 



Nov., 1940] COMMERCIAL 16-MM PRODUCTION 465 

materials, and services that are available to the direct 16-mm pro- 
ducer today enable him to turn out a result at least as good from a 
technical standpoint as the results that have been obtained in the 
past by optical reduction from 35-mm negatives. The usefulness of 
direct 16-mm production lies in the fact that it makes this quality 
available at greatly reduced cost, thereby making it possible for busi- 
ness and education to employ motion pictures on an extended scale 
which has long been recognized as desirable, but which by previous 
methods has been found too costly to be practical. 

REFERENCES 

1 BENFER, R. W.: "A 16-Mm Studio Recorder," /. Soc. Mot. Pict. Eng., 
XXXII (May, 1939), p. 534. 

2 MAURER, J. A.: "The Present Technical Status of 16-Mm Sound-Film," 
/. Soc. Mot. Pict. Eng., XXXHI (Sept., 1939), p. 315. 



ADVANCEMENT IN PROJECTION PRACTICE* 
F. H. RICHARDSON** 



Summary. A brief review of projection practice from the beginning, pointing 
out the extremely poor conditions confronting projectionists in early days. Early 
projection equipments are illustrated and contrasted with those in use today. The 
work of some of the outstanding pioneers who had to do with early invention and im- 
provements in projection equipment is described. 



It has been suggested that I prepare for presentation at this gather- 
ing, as a part of the projection session, an outline of the advancement 
made in presentation of the finished product of our industry to its 
purchaser, the public in other words, in projection and its prac- 
tices from the earliest days until now. 

The task of preparing this paper was undertaken without con- 
sideration of the wide research required to obtain and verify all the 
data that would be necessary to make such a record complete. More- 
over, if anything like a complete record were required, the presenta- 
tion would consume far more time than a meeting such as this could 
possibly afford. 

An attempt has been made therefore to supply only a few of the 
highlights of the advances made in projection, and some of the dates 
provided should be regarded as only closely approximate. Further- 
more, it should be understood that this record has to do only with 
projection in the United States. Space limitations prevent con- 
sideration of the notable pioneer work of many projectionists and 
equipment manufacturers in Europe, or the splendid accomplish- 
ments of pioneers in allied fields, such as, for example, Louis Lumire, 
in France; Robert Paul, in England; Oskar Messter, in Germany; 
or of W. K. L. Dickson, who assisted Thomas A. Edison in the vast 
amount of research that finally produced a practicable motion picture 
camera, as well as many others who assisted in bringing our great 

* Presented at the 1940 Spring Meeting at Atlantic City, N. J. ; received 
May 1, 1940. 

** Quigley Publishing Co., New York, N. Y. 

466 



ADVANCEMENT IN PROJECTION PRACTICE 



467 



industry into existence and building it into the splendid thing it is 
today. 

But when we attempt to look back through the mists that shroud 
the years as soon as they pass into history, growing denser from 
year to year, we find many details hidden wholly from view, and 
others are seen but indistinctly, which emphasizes the importance 
of making authentic records of outstanding events at the time of 
their occurrence. 

Those of us remaining who still have some first-hand knowledge of 
the introduction of the motion picture into the theatrical field feel 
amazed at the rapid advancement and vast improvement achieved 



Raff $ Gammon 




ftojtbury, K&a*. 
Br. Sir:- 

Replying to your jtoctal cord of 
tht th right to Massachusetts has been 
blfcit in that state, you *JU have to add 
Xlfbr, 419 Kw M&rket St., FMladelpM 

Woali be gl,\a to sell you th right 
open, but they *re nearly all tkn nd 
lh to or euch a right. 

Very truly yor 



10 5th Scat., we beg to aay 

d, an<J Jf yew wish to x- 

! th purch&eer, Ur. V* W. 

Pa. 

sny atftt reaslnlng 

. should &ot promptly Jf y 



FIG. 1. 



Original letterhead of Raff & Gammon featur- 
ing the "Vitascope". 



in the presentation of life-size motion pictures to theater audiences 
since its first successful introduction in the United States at Koster & 
BiaTs Music Hall on 34th Street, West of Broadway in New York on 
the evening of April 23, 1896. The projector used that day was a 
so-called Edison Vitascope, which upon that occasion was in charge 
of Mr. Thomas Armat who had built and designed it himself. It 
had what is known as a "beater" intermittent movement. This 
projector had been previously used to give a demonstration to Messrs. 
Raff and Gammon in the Postal Telegraph Building, 253 Broadway, 
New York. This firm was managing the exhibitions of the Edison 
peephole projector, then used considerably for showing miniature 
motion pictures. The name "Vitascope" was given the projector 
by Mr. Armat. Its patent number is 673,992. 



468 



F. H. RICHARDSON 



[J. S. M. P. E. 



Subsequently Mr. Armat developed and patented another pro- 
jector mechanism in which was incorporated the star or Geneva-cross 
intermittent movement which is now, in greatly refined form, in 
use in motion picture projectors throughout the world. This mecha- 
nism was covered by U. S. Patent No. 578,185, filed and published 
March 2, 1897. 

Armat therefore was not only the inventor of the first satisfactory 
intermittent movement, as applies to motion picture projectors, but 




FIG. 2. The first "motion picture theater," New Orleans, La. ; second from 
left, William Reed, projectionist; fourth and fifth from left, William Rock and 
Walter Wainwright, proprietors. 

was the first to project motion pictures successfully before a theater 
audience in this country. He is of right entitled to be hailed as 
father of the motion picture projector as we know it today. Al- 
though the years have added very many refinements, the basic prin- 
ciples of the projector have not been altered. Mr. Armat still 
lives, in the city of Washington, D. C. 

The events leading to the production of a really practicable motion 
picture projector are, so far as ascertainable, as follows: First, a 
showing of motion pictures, approximately life size, was staged by 
Armat and C. Francis Jenkins, founder of our Society, at the Cotton 
States Exposition, Atlanta, Ga., 1895. The projector, however, 



Nov., 1940] ADVANCEMENT IN PROJECTION PRACTICE 469 

lacked a framing device. It had no provision for the loops, so neces- 
sary for successful projection. It had an intermittent movement 
that was found to be impracticable for commercial use. 

Later Armat remodeled the mechanism, retaining the beater 
movement but adding provision for forming the loops. This was 
the mechanism used for demonstration before Messrs. Raff and 
Gammon in 1896, and afterward used at Koster & Bial's Music Hall, 
where its performance was loudly cheered by the audience. 

Still later, not satisfied with the beater type of intermittent move- 
ment, Armat modified the Geneva-cross movement, long used for 
other purposes, to essentially its present form, and installed it in 
his Vitascope. Armat's Vitascope intermittent employed one cam- 
actuating pin. Later Edison, for some inexplicable reason, added a 
second pin to the driving cam, but, later still, finding it very in- 
efficient as compared with the one-pin movement, he withdrew it 
and returned to the original Armat one-pin movement. So far as 
I can recollect or ascertain, no other projector manufacturer adopted 
the two-pin movement. The one-pin movement enabled the use of 
a three-bladed rotating shutter, which with the relatively low pro- 
jection speed (60 feet of film per minute) then in use was necessary 
to eliminate flicker. It gave the film a smooth, gradual accelerated 
start-and-stop movement and worked wonders in the reduction of 
stresses at the film sprocket-holes and of eye-straining flicker by 
enabling the use of either a two- or three-bladed shutter. 

After witnessing a demonstration of Armat's projector, Edison 
agreed to manufacture it. However, Edison was convinced, as 
was almost everyone else at the time, that the motion picture was 
merely a novelty and would die out as soon as it ceased being a 
novelty. First production was limited to fifty projectors, instead 
of the eighty demanded by Raff and Gammon. The projector was 
called the "Edison Vitascope" because Messrs. Raff and Gammon 
believed that Edison's name would have commercial value, and also 
because the Edison Company was to furnish the necessary films, and 
Edison held patents or applications for patents controlling both the 
films and the camera for making the picture. 

No satisfactory means was provided on the first projectors for 
framing the picture. Later, Albert E. Smith, one of the partners 
in the Vitagraph Company, while experimenting with a frictional 
feed projector with (it is believed) an idea of avoiding the Edison 
perforated film patent, developed the framing device essentially as 



470 



F. H. RICHARDSON 



tf. S. M. P. E. 



we now know it. He patented it as U. S. Patent No. 673,329, dated 
April 30, 1901. Prior to this, framing was accomplished by means 
of a picture-size, sliding frame, which was all right in a way but 
threw the picture off the optical axis and was otherwise not so satis- 
factory as the Smith device. 

Fig. 1 shows a letter written by Messrs. Raff and Gammon. For 
reasons already explained the projector went forth as the "Edison 
Vitascope" and was introduced on a state rights basis. This letter 




FIG. 3. Side views of one of the first projectors. 



shows plainly the avidity with which the state rights were snapped 
up. 

Let us now turn to things directly connected with projection, dis- 
regarding sound as being too new to be regarded in any way as his- 
toric. 

As already stated, the first showing of life-size motion pictures in 
acceptable form in a theater occurred at Koster and Bial's Music 
Hall on May 23, 1896. The first theater to open its doors as a purely 
motion picture theater at least the first of which any authentic 
record can be found began business in midsummer at 623 Canal 
Street, New Orleans, La. Fig. 2 is a photograph of the "theater." 



Nov., 1940] ADVANCEMENT IN PROJECTION PRACTICE 



471 



Its owners, William Rock and Walter Wainright, stand at the right. 
Mr. Rock was later one of the partners in the Vitagraph Company, 
one of our early-day film producers. 

The little theater was an ordinary store room, equipped with an 
unbordered cloth screen and ordinary wooden kitchen chairs. The 
projector was on a raised platform, surrounded by a cloth curtain. 
Mr. William Reed, who is with us today and who has been continu- 
ously projecting motion pictures since that time, was the "operator." 




FIG. 4. Intermittent sprocket of the projector 
shown in Fig. 3. 



Looking back we can not but feel justifiable pride in the fact that 
from an extremely lowly beginning projection has advanced to a plane 
of excellence commanding attention and respect from all. Not only 
have the results presented to the theater audiences advanced wonder- 
fully in point of excellence, but the "operator," who in the beginning 
represented perhaps the least respected item in all the industry's 
personnel, has himself advanced to a plane where those who respect 
themselves and the work in which they are engaged are well con- 
sidered and treated with respect. No longer are they looked upon 
as merely operators of a machine. Instead they are accorded the 



472 



F. H. RICHARDSON 



[J. S. M. P. E. 



respect due to men possessed of the wide range of ability and knowl- 
edge requisite to competent handling of the intricate, finely adjusted 
modern projection installation. He is no longer known as 
"operator," but as "projectionist." 

In the beginning the "machine operator" knew almost nothing 
about projection and its problems; in fact, he did not conceive of 




FIG. 5. Powers No. 3 projector. 



projection as having any problems. Anyone who knew how to make 
a crude film splice, trim a lamp, thread a film into the projector, and 
do the rewinding, was regarded as equipped with all the knowledge 
required. 

Everything with which he was provided to do the work was almost 
primitive in design and crude in construction, and the film was poor, 
of uneven thickness and unevenly perforated. 



Nov., 1940] ADVANCEMENT IN PROJECTION PRACTICE 



473 



Illustrative of the primitive equipment is the machine shown in 
Fig. 3, a very early mechanism made by A. A. Heldt, of Evansville, 
Indiana. Fig. 4 is a close-up of the intermittent sprocket. 

Fig. 5 shows the first model of the celebrated Powers projector, 
put forward under the trade name "Powers Peerlescope." It was 
made in 1902 by Nicholas Power, in a tiny shop located on Nassau 
Street, in New York City. This projector was equipped with a gas- 
light source, and was belt-driven, directly from the rim of the crank- 
wheel. . It had tiny, telescoping legs and a cloth bag, into which the 



N0.1A 




FIG. 6. (Left} Early Edison projector equipped for gas; (right) Nos. 1, 2, 
and 3, Optigraph; No. 1A, Motiograph. 



film dropped after having passed through the mechanism. In the 
later models some city authorities banned the cloth bag, demanding 
its replacement by a sheet-metal tank or box some three feet high. 
The projector lamp house and mechanism were attached to a wooden 
board, usually of black walnut, which then was attached to the top 
of the tank, the supporting legs being omitted. 

The film entered the tank through a rectangular opening under the 
mechanism. This opening was fitted with a sliding metal cover, 
held in the open position against a coiled spring, into the holding 
wire of which a fuse link was connected. Into these tanks as many 
as three 1000-foot reels of film were often run in a loose heap. In 



474 F. H. RICHARDSON [J. S. M. P. E. 

most cases there was but one projector in each theater. Theater 
owners, at least in the Middle West, had insufficient confidence in 
the motion picture as a form of amusement to risk the expense of 
installing a second projector. Audiences therefore had to sit in 
darkness at the end of each reel while another reel was threaded up, 
the lamp trimmed, etc. Great haste on the part of the projectionist 
was, of course, demanded. Usually he would remove a carbon stub 
and lay it on top of the tank, whence it could roll through the open- 

For Alternating Currents 




Guaranteed to save two-thirds on electric bill on 
110 volts, and over 80 per cent.' on 220 volt?/ Also 
guaranteed for one year against im-charucal and 
electrical defects, 

FIG. 7. The Hallberg "Economizer." 

ing and drop into the pile of loose film ; and if it were hot a fire would 
occasionally result. In case of a fire the fuse would melt and the 
cover of the opening would snap shut. Since there was no other 
opening save a door in the side held shut by a substantial metal latch, 
and since the mass of burning film generated great quantities of gas, 
either the door would blow off or the tank would blow up. That is 
where newspapers acquired the idea that film was explosive. 

The tail end of each reel was left hanging out of the opening to be 
retrieved for rewinding. If, as sometimes happened, it slipped into 
the tank, the "operator," who had to rewind in the limited time 
between shows, was faced with a very real trouble. However, it 



Nov., 1940] ADVANCEMENT IN PROJECTION PRACTICE 475 

was rather astonishing to see how smoothly a 1000-foot length of 
film would pull out of a 3000-foot loose pile, at high speed, with but 
rare inclination to tangle. 

There were two things over which projectionists of earlier days 
had no control that made even passable excellence in results wholly 
impossible. They were, first, a combination of inaccuracy of film 
perforation and, second, a great lack of mechanical accuracy in 
projector mechanisms, particularly the intermittent sprocket and 
intermittent movement. The condition in this respect was so bad 
up to about 1910 that the screen image was seldom steady during the 
projection of three consecutive feet of film. 

The engineers of the projector-manufacturing companies deserve 
the highest credit for the improvements they have accomplished 
during the ensuing years. Today we often view a production 
critically scarcely being able to detect the slightest movement of 
the screen image as a whole. Other credit must go also to the carbon 
manufacturers. In the beginning we had nothing but ordinary 
carbons such as were used for street-lighting arc lamps. They were 
chock full of various impurities; they were not accurately straight; 
they were filled with hard and soft spots and cracks. The screen 
illumination was unsteady, variable in tone, and likely to fail entirely 
without an instant of warning. 

About 1910 the demand for carbons for projection became so great 
and the demand for improvement so insistent that a continuous line 
of development immediately followed. Today we have a light- 
source that is extremely steady, and a screen illumination of dazzling 
whiteness. 

The lens manufacturers also have contributed to the development, 
with faster lenses of wider aperture, and most recently, the new 
coated lenses for inhibiting surface reflections. Sharp, clear images 
magnified from an area of less than one square-inch to as much as 
18 X 24 feet are usual today. 

To illustrate the strides that have been made, Fig. 6 shows 
projectors such as were used in early days. Barring a few wires 
and one or two switches this picture shows everything that most 
projection installations included, except possibly a stereopticon, 
even as late as 1907. The machine on the left is an Edison machine 
equipped for gas. Note the thin, weak, adjustable legs and 
the small lamp house. At the right are Motiograph models of ap- 
proximately the same date: Nos. 1, 2, 3, and 1A, early examples of 



476 



F. H. RICHARDSON 



[J. S. M. P. E 







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Nov., 1940] ADVANCEMENT IN PROJECTION PRACTICE 



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478 



F. H. RICHARDSON 



[J. S. M. P. E. 








Nov., 1940] ADVANCEMENT IN PROJECTION PRACTICE 



479 




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480 



F. H. RICHARDSON 



[J. S. M. P. E. 



high-accuracy projector construction. Another projector of this 
period, called the Kinedrome, was put out by a Chicago company. 
It was not placed on sale, but was rented to theaters, together with 
an operator and a supply of film. 




FIG. 16. The Viascope, marketed to a limited 
extent by the Vitagraph Corp. about 1908-10. 



Up to about 1909 the alternating current for motion picture pro- 
jection light-sources had been controlled wholly by rheostats, which 
not only wasted power but were difficult to handle. In that year, 
J. H. Hallberg, a New York City supply dealer, produced the "Hall- 
berg Economizer" (Fig. 7), a low- voltage transformer. Alteration 
of its connections made it capable of supplying three different values 
of current to the arc, at the same voltage. It immediately became 
very popular, and hundreds of them were placed in the theaters. 



Nov., 1940] ADVANCEMENT IN PROJECTION PRACTICE 



481 



This transformer was the first step forward in an improved alternat- 
ing-current light-source. 

It has been found impossible to obtain photographs of the very 
early Edison kinetoscope. However, through the courtesy of the 
Historical Research Organization of Thomas A. Edison, Inc., Figs. 
8 and 9 were obtained. These show the "Exhibition Model," re- 




FIG. 17. Lubin Cineograph; discontinued about 1910, 

leased in 1898 and kept on the market until Mr. Edison's final re- 
tirement from the projector manufacturing field about 1914. 

Fig. 10 shows the Edison Type B mechanism. The exact date on 
which this was placed on the market is not certain, although it must 
have been about 1909. It had a metallic supporting frame and 
several other minor improvements as compared with the Exhibition 
Model. Each of these models served a wide field and gave what was 
regarded as good service in that day. 



482 



F. H. RICHARDSON 



[J. S. M. P. E. 



About 1914 Edison developed a model that was marketed under 
the trade-name Edison Super-Kinetiscope. However, upon its 
theater try-out some rather serious faults developed. Also about 
this time a bad fire occurred at the Edison plant, and many jigs, 
dies, etc., necessary to the manufacture of projectors were destroyed. 
Mr. Edison was then engrossed in his notable storage battery re- 
search, and sold his complete projector manufacturing interest to 




FIG. 18. A modern projector, by way of contrast. 

the Baird Machine Company, which at that time was growing rapidly 
in the projector manufacturing field, but later discontinued upon the 
death of its founder, Mr. Baird (abouc 1914). 

Figs. 11 to 17 show a number of other early projector mechanisms. 

One important development must not be overlooked. In 1909 
Nicholas Power started experimenting on a wholly new type of 
intermittent movement, which finally appeared in the Powers Six 
mechanism, released to the trade early in 1911. This movement was 
withdrawn after the consolidation of the Powers Company and the 
Precision Machine Company, the latter being the manufacturers 



Nov., 1940] ADVANCEMENT IN PROJECTION PRACTICE 483 

of the Simplex projector. However, the Powers movement was 
acclaimed by projectionists as the best movement ever delivered to 
them. 

In Fig. 18 is shown a modern projector, showing the contrast be- 
tween the old machines and the splendid equipment we now have. 

Some of the outstanding pioneers in the American field of pro- 
jection should be named before closing: Thomas Armat, who in 
1895 made life-size motion pictures possible by introducing into the 
projector mechanism the Geneva cross; Thomas A. Edison, who took 
over the manufacture of the Armat inventions and put them on the 
market; Nicholas Power, who accomplished a great work in improv- 
ing the projector; A. C. Roebuck, who demonstrated the improve- 
ment in results that could be achieved by accurate mechanical con- 
struction of projector mechanisms; Frank Cannock and E. S. Porter, 
the former notable for his constructive work in improving the pro- 
jector, the latter for making Mr. Cannock's work possible by financial 
backing as well as for advancing many ideas himself. It was these 
men who paved the way toward the modern projector. 

One important feature of the projector development should not 
be overlooked: namely, the substitution of the outside for the inside 
shutter, later removed from in front of the projection lens and placed 
between the light-source and the aperture, where it functioned 
equally well from the optical viewpoint and reduced the heat at the 
aperture by fifty per cent. Finally came the combination front and 
rear shutter, which reduced the time of occultation of the light-beam 
and added considerably to the amount of light delivered to the screen. 
Next in importance perhaps was the substitution of a solid, rigid 
supporting base for the entire projector. One might continue in- 
definitely to itemize the improvements that have occurred in pro- 
jection, but as the finishing touch we have, of course, addition of 
sound to the picture about 1929, and the consequent great elabora- 
tion of the projection equipment. 



THE ELIMINATION OF HYPO FROM PHOTOGRAPHIC 

IMAGES * 



J. I. CRABTREE, G. T. EATON, AND L. E. MUEHLER** 



Summary. It is very difficult, if not impossible, to remove the last traces of hypo 
from photographic papers by any known procedure of washing. The sulfur in the 
residual hypo ultimately, and especially under abnormal conditions of temperature 
and humidity, combines with the silver image to form yellowish-brown silver sulfide. 
This phenomenon is known as sulfiding or "fading" of the image. The various 
factors which affect the rate of fading of images and the washing out of hypo from 
films and papers are outlined. 

Chemical methods of hypo elimination have been proposed from time to time but 
the majority of these have not been satisfactory because they tend to leave substances 
such as thionates in the photographic material, which are equally as difficult to wash 
out as hypo and which also tend to sulfide or fade the silver image. A new hypo 
eliminator is recommended consisting of two volatile chemicals, hydrpgen peroxide 
and ammonia. This eliminator oxidizes the hypo to sodium sulfate, which is inert 
and soluble in water, while any excess eliminator evaporates on drying. 

Two formulas and treatments are proposed: (1) Complete elimination of hypo 
for use by the professional, advanced amateur, and photofinisher who demand the 
highest standard of photographic quality in their prints. (2) Almost complete 
elimination of hypo (less than 0.01 milligram per square inch). Since the conditions 
to which prints will be subjected are rarely known in advance, use of the "complete 
elimination treatment" is advised in all cases. 



In the processing of photographic developing-out materials such 
as gelatin silver emulsions coated on paper, film, or glass supports, 
if after fixation, the hypo (sodium or ammonium thiosulfate) is not 
completely eliminated from the processed material by washing or 
other means, under suitable conditions of temperature and humidity 
during storage, the silver image will tend to "fade." 

This fading is a result of the conversion of more or less of the silver 
image to silver sulfide by the sulfur present in the residual hypo, 
and is manifest by a change in hue of the image first to yellowish 

* Communication No. 780 from the Kodak Research Laboratories. Presented 
at the October, 1940, meeting of the Photographic Society of America, at Cleve- 
land, Ohio (/. Phot. Soc. Amer.. VI (October 25, 1940)), p. 6. 
** Eastman Kodak Co., Rochester, N. Y. 

484 



ELIMINATION OF HYPO FROM IMAGES 485 

brown, then to yellow and, in most cases, the change is accompanied 
by a yellowing of the unexposed portions of the image. This yellow- 
ing of the highlights is a result either of (a) the use of an exhausted 
fixing bath, or (b) insufficient fixation whereby complex silver-sodium 
thiosulfates are retained and, under the proper conditions, decompose 
to give yellow silver sulfide. 

In addition to attack of the silver image by hypo within the gelatin 
layer, many external agents are also effective, the most significant 
being hydrogen sulfide which is present in coal gas (illuminating 
gas). High humidity and temperature accelerate this reaction 
tremendously. Sulfur dioxide and other acid gases, in the absence of 
hypo, affect the silver image to a much less degree than hydrogen 
sulfide. 

The rate at which a silver image fades depends upon many factors, 
including (1) the concentration of hypo (or tetrathionate) in the 
image layer, (2) the concentration of hydrogen sulfide and other acid 
gases in the atmosphere, (3) the grain size of the silver image, and 
(4) the temperature and humidity of storage. 

Tests have shown that the degree of fading in a given time is 
roughly proportional to the concentration of hypo up to a certain 
limit, and a concentration as low as 0.005 milligram per square-inch 
may cause fading with fine-grained images, especially in the case of 
papers. 

An increase in the humidity, temperature, or both accelerates the 
rate of fading, and a combination of high humidity and high tem- 
perature, which conditions usually exist in tropical countries, is fatal 
to a photographic print containing hypo. 

The presence of saline matter and acidic gases in the atmosphere 
also tends to increase the rate of fading. 

Since fading or sulfiding of the image must necessarily take place 
initially at the surface of the image grains, fine-grained emulsions 
will tend to fade much more rapidly than coarser-grained emulsions 
and, in practice, chloride paper emulsions give images which are much 
more susceptible to fading than bromide emulsions. Similarly, a 
fine-grained positive transparency is much more susceptible to fading 
than an image on a high-speed negative emulsion. 

Sodium thiosulfate tends to oxidize when exposed to the air with 
the formation of thionates and some sulfate. Certain recommended 
hypo eliminators oxidize hypo to sodium tetrathionate but the 
presence of this compound (and probably other thionates) is harmful 



CRABTREE, EATON, AND MUEHLER [j. s. M. p. E. 



because tetrathionate causes sulfiding of silver images almost as 
readily as hypo. 

During this investigation it was essential to use an accelerated 
fading test in order to obtain directly comparable results within a 
reasonable time. Crabtree and Ross 1 have recommended the 
storage of test strips in a sealed glass container over water stored at 
a temperature of approximately 110F. In the present investigation 




FIG. 1. Apparatus for accelerated fading tests. 

these storage conditions were maintained, the strips (negatives and 
prints) being suspended on glass rods in sealed glass containers, as 
shown in Fig. 1. 

THE ESTIMATION OF HYPO IN PHOTOGRAPHIC MATERIALS 

A fallacy of the majority of investigations on hypo elimination has 
been the attempted estimation of the residual hypo by measurement 
of the hypo contained in the wash water. Testing solutions usually 
employed for this purpose are alkaline permanganate, iodine-azide, 
and mercuric chloride. These methods give a fairly accurate meas- 



Nov., 1940] ELIMINATION OF HYPO FROM IMAGES 487 

lire of the effect of washing upon "readily diffusible hypo" but they 
give no indication of the quantity of hypo retained by the photo- 
graphic material. 

In the case of images on glass or film, the hypo is usually removed 
quite readily by washing but, in the case of paper prints, it is ex- 
tremely difficult, if not impossible, to remove all traces of hypo by 
washing alone. Apparently the thiosulfate ion is tenaciously held 
by the paper fibers and the baryta coating. A quantitative deter- 
mination of the residual hypo in the photographic materials them- 
selves is therefore necessary. 

In 1908, Lumiere and Seyewetz 2 recommended the use of silver 
nitrate as a spot test on prints and, again in 1935, Weyde 3 suggested 
the treatment of prints with silver nitrate to determine the hypo 
concentration but no details of a quantitative standardization were 
given. 

In the present investigation, the silver nitrate test was standardized 
in such a manner that the transmission density of a print bathed in 
silver nitrate was proportional to the quantity of hypo contained in 
the print and quantities as low as 0.005 milligram of hypo per square 
inch were determined successfully. The data obtained were also 
confirmed by a quantitative determination of the reducible sulfur in 
the paper. 4 With this method as a tool, a much more direct com- 
parison of the effectiveness of many suggested "hypo eliminators" 
was possible. 

With the usual permanganate test which consists in allowing the 
surplus water from a washed single-weight print to drain into a 
solution of potassium permanganate, a zero test is obtained when 
the silver nitrate test indicates the presence of about 0.2 milligram of 
hypo per square inch, a quantity which is capable of producing an 
objectionable degree of fading. 

To determine the hypo in film, the mercuric chloride-potassium 
bromide test recommended by Crabtree and Ross 5 was used. A 
square-inch of the material is placed in 10 cubic-centimeters of the 
reagent and, after 15 minutes, the turbidity is compared with the 
turbidity produced in a series of standard solutions. This test ac- 
curately measures quantities of hypo in films as low as 0.005 milli- 
gram per square-inch. 

The mercuric chloride reagent was applied to prints but found in- 
capable of reacting with all of the hypo in the sample. Since only 
the hypo which diffuses out of the film or print contributes to the 



488 CRABTREE, EATON, AND MUEHLER [j. s. M. P. E. 

opalescence, the test measures only the "readily diffusible" hypo, 
whereas in the silver nitrate test, the silver nitrate reacts with all of 
the hypo within the film or print. Comparison of the results obtained 
with the mercuric chloride and the standardized silver nitrate test 
with prints is given in Table I. 



TABLE I 



Comparison of Mercuric Chloride and Silver Nitrate Test with Photographic Prints 



Washed Prints (Minutes) 
Single- Double- 

Weight Weight 

15 
30 
60 

15 
30 
60 



Hypo Content 
(Mg per Sq In) 

Mercuric Silver 

Chloride Nitrate 



0.004 

0.01 

Trace 

0.02 

0.01 

Trace 



0.073 
0.042 
0.020 
>0.320 
0.173 
0.134 



THE ELIMINATION OF HYPO BY WASHING 

The washing of photographic materials has always been accepted 
as a necessary operation but the importance of removing the last 
traces of hypo has often been underestimated. 

Negatives. For washing it is always preferable to use running 
water in a system such that an "ideal stream" prevails, that is, a 
sufficient volume of water passes over the surface of the material so 
that it removes the hypo from the surface of the emulsion faster than 
the hypo diffuses out. When washing in a tray in still water, the 
water must be changed often and the negatives agitated continually. 
Under ideal conditions of water renewal, the most important factors 
which affect the rate of washing of films are: (1) the temperature 
of the wash water, and (2) the composition of the fixing bath. 

The curves in Fig. 2 illustrate the effect of the temperature of the 
wash water on the rate of elimination of hypo from Eastman Veri- 
chrome film. The films were washed under "ideal" conditions of 
water flow and it is seen that a change in temperature from 40 to 
65F increases the quantity of hypo removed in a given time of wash- 
ing by about 33 per cent, whereas increasing the temperature from 65 
to 80F almost doubles the quantity of hypo removed. A tempera- 
ture of 60 to 70F is recommended in view of the danger of swelling 
and softening at higher temperatures. 



Nov., 1940] 



ELIMINATION OF HYPO FROM IMAGES 



489 



The hypo was also more readily washed from film which had been 
fixed in a nonhardening fixing bath than from film fixed in a potassium 
alum fixing bath. The use of a chrome alum fixing bath resulted in 
washing times somewhat less than those for potassium alum-hard- 
ened negatives. 



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10 20 30 

WASHING TIME IN MINUTES 



40 



FIG. 2. Effect of wash water temperaure on rate of 
hypo elimination from Eastman Verichrome Film. 

Prints. Thorough washing is much more important in the case 
of prints than with negatives because fine-grained paper emulsions 
fade much more readily and, in some cases, in the presence of as small 
a quantity of hypo as 0.002 milligram per square-inch. Not only 
is the image more susceptible to fading but relatively high concen- 
trations of hypo are usually retained in the print. This retention of 
hypo is due to the presence of the paper fibers and the baryta coating 
and, since, even with extremely long times of washing with an 
"ideal stream of pure water," traces of hypo are retained in prints 



490 



CRABTREE, EATON, AND MUEHLER [j. s. M. p. E. 



(especially with double- weight stock), it is apparent that the thio- 
sulfate ion is probably mordanted or adsorbed to the fibers and 
baryta. 

As in the case of negatives and assuming an "ideal stream" for 
washing, the two most important factors to be considered in the 
elimination of hypo from prints are : (1) the temperature of the wash 
water, and (2) the composition of the fixing bath. 

In 1908, Lumiere and Seyewetz 6 and in 1910, Hauberrisser 7 
recommended the use of elevated temperatures during washing but, 




20 40 60 50 100 120 140 160 100200 220240260260300320340360380 
WASHING TIME IN MINUTES 

FIG. 3. Effect of temperature of wash water on rate of elimination 
of hypo from single and double-weight prints. 

to date, no extensive practical application has been made of the sug- 
gestion. The curves in Fig. 3 show the effect of the temperature of 
the wash water on the rate of elimination of hypo from single and 
double-weight prints. 

Single and double-weight papers were washed for 20 hours, but 
the curves indicate that a maximum elimination is approached after 
1 or 2 hours. The very great effect of temperature of the wash water 
is evident for the shorter washing times but is not so great for the 
longer times of washing. Washing for as long as 20 hours did not 
eliminate the last traces of hypo in either single or double-weight 
papers. With extended washing, the rate of elimination tends to 
approach zero. The quantities of hypo retained after prolonged 



Nov., 1940] 



ELIMINATION OF HYPO FROM IMAGES 



491 



washing are sufficient to cause fading under certain storage condi- 
tions. It is evident, therefore, that use of a hypo eliminator is a 
necessity if the highest degree of permanence is desired. 

The prints shown in Fig. 4 were washed for times sufficient to leave 
the designated quantities of hypo in them and were then stored under 





0.250 m<^. HYPO per s<$ in. 



100 mq, HYPO per sq. in. 







0.01 mq HYPO per. sq. in, 



UNTREATED 



FIG. 4. Accelerated fading tests illustrating the relative fading pro- 
duced by decreasing concentrations of hypo. (Hypo content in milli- 
grams per square-inch chloride emulsion.) 



the accelerated fading conditions previously described. They illus- 
trate the effect of increasing hypo concentration on the degree of 
sulfiding or fading of the image and emphasize the necessity for the 
complete elimination of hypo from papers coated with fine-grained 
chloride emulsions. 



492 CRABTREE, EATON, AND MUEHLER [j. s. M. p. E. 

HYPO ELIMINATORS 

The term "hypo eliminator" was first used by Hart 8 to indicate a 
solution which was capable of oxidation of thiosulfate to neutral sul- 
fate. Oxidizing agents only were known as eliminators but the term 
acquired general use and is now applied to any solution or chemical 
that either oxidizes the hypo or assists in its elimination. 

Many chemical treatments have been proposed to assist in the 
elimination of hypo or to make photographic prints permanent. 
Some of these may be listed as follows: alum (1855) ; hypochlorous 
acid (1864); hydrogen peroxide (1866) ; sodium hypochlorite (1866); 
ammonium carbonate (1866); iodine (1872); zinc hypochlorite 
(1881), known as Flandreau's eliminator; ammonium persulfate 
(1899); potassium percarbonate (1901); alkaline perborates (1903) ; 
potassium permanganate (1904); chloramine T (1922); alkali car- 
bonate or phosphate (1923) ; dilute caustic soda (1925) ; peroxide and 
ammonia (1931); and 1 per cent sodium carbonate (1935).* None 
of the suggested treatments has been generally accepted nor has any 
stood the test of time. It has been shown that none of these recom- 
mended treatments, even when used following careful washing, was 
effective enough to eliminate the hypo completely. In several 
instances increased concentration of the constituents successfully 
oxidized the hypo but to the detriment of the silver image. 

Two general types were found to be particularly effective, namely, 
(a) alkalies, and (b) oxidizing agents such as hydrogen peroxide- 
ammonia solutions. 

Alkalies. Norton and Crabtree,** working with paper prints, 
recommended the use of dilute sodium carbonate solutions im- 
mediately after the fixation process and previous to washing. How- 
ever, in view of the danger of precipitation of alumina with fixing 
baths containing alum, it is considered desirable to wash negatives 
or prints before the alkali treatment. 

(1) Negatives. Various alkalies were found to assist in the 
elimination of hypo from negatives but they were not equally effec- 
tive. A quantity of film was normally processed and washed for 8 
minutes at 65F in running water, samples then being treated in 
distilled water, ammonium hydroxide, Kodalk, sodium hydroxide, 
and sodium carbonate solutions (0.3%) for 2 minutes. These samples 

* A chronological bibliography is given in the appendix. 
** Eastman Kodak Laboratories, July, 1923, unpublished results. 



Nov., 1940] ELIMINATION OF HYPO FROM IMAGES 493 

were washed for 2 minutes, dried, and analyzed by the mercuric 
chloride method which indicated the following hypo contents in 
milligrams per square-inch : 

Mg per Sq-In 

Untreated >0.06 

Distilled water . 02 

Ammonium hydroxide (0.3%) pH = 10.40 Nil 

Kodalk (0.3%) pH = 9.90 0.01 

Kodalk (0.3%) pU adjusted to 10.40 0.005 

Sodium hydroxide (0.3%) pH = 11.57 0.01 

Sodium hydroxide (0.3%) />H adjusted to 10.40 0.01 

Sodium carbonate (0.3%) pH = 10.48 0.005 

Ammonium hydroxide was the most effective alkali and it also 
had the least effect on the physical properties of the emulsion. In 
most instances, regardless of the alkali, the time required to wash out 
the hypo completely was reduced by more than 50 per cent. 

2. Prints. An extensive study of the use of alkalies with respect 
to the elimination of hypo from prints indicated that ammonia was 
the most effective alkali. Sodium metasilicate, sodium hydroxide, 
and ammonia at concentrations of 0.08 Molar* caused the complete 
elimination of hypo from prints which had been washed in an "ideal" 
stream of water for 15 minutes at 65 to 70F, but the hydroxide 
and metasilicate produced severe physical defects in the print. 
Ammonia could be effectively used at room temperature and did not 
damage the prints. However, the time of 45 minutes required for 
treatment was excessive. 

Peroxide- Ammonia: (1) Negatives. The use of hypo elimina- 
tors, other than alkalies, is not usually required in the processing of 
negative materials. However, the hydrogen peroxide-ammonia 
eliminator recommended below for prints is applicable to film emul- 
sions also but must be used in lower concentrations (diluted 1:10) 
because of the tendency to soften and blister the emulsion. 

(2) Prints. The outstanding fault with the majority of oxidizing 
agents proposed for hypo elimination is their acid character or their 
need for an acid medium. An alkaline peroxide solution, on the 
other hand, is a very effective oxidizing agent for sodium thiosulfate 
and does not attack the silver image even in quite high concentra- 
tions. 

* In grams per liter sodium metasilicate (crystal) 17 grams; sodium hy- 
droxide, 3.2 grams; ammonia (28%), 5 cubic-centimeters. 



494 CRABTREE, EATON, AND MUEHLER [j. s. M. p. E. 

Hydrogen peroxide itself was recommended as early as 1866 by 
Smith 9 to be used in a dilution of 1:1000 for a minute or two. He 
later suggested that the acid in the peroxide be neutralized with 
soda. About the same time Spiller 10 reported an attempted use of a 
mixture of hydrogen peroxide with ammonia but declared that such 
a mixture was unsatisfactory because the two constituents "mutually 
decomposed." Subsequent workers reported that hydrogen per- 
oxide itself did not oxidize all of the hypo to sulfate but produced 
some thionates. This is actually the case but alkaline peroxide 
having a suitable H value oxidizes the thiosulfate completely to 
sulfate. 

In 1931, a note in Das Lichtbild 11 mentioned the use of hydrogen 
peroxide as a hypo eliminator. Here, ammonia was added dropwise 
until the solution just smelled of ammonia, an adjustment which 
corresponds to that of Smith who used soda to neutralize the acid in 
the peroxide. It is evident, then, that the previous use of hydrogen 
peroxide was concerned with neutral hydrogen peroxide. 







TABLE II 




Change in pH with Increased Ammonia Concentration 


H 2 2 (3%) 


Composition of Solution 
(Cc per Liter) 
Water 


Ammonia (28%) 


pn 

Glass Electi 


500 


500 




3.7 


500 


500 


0.6 (Das Lichtbild} 


9.0 


500 


500 


2.0 (Marked odor) 


9.3 


500 


500 


10.0 


9.8 


250 


750 


10.0 


9.95 


125 


875 


10.0 


10.15 




1000 


10.0 


10.75 



Experiments in these Laboratories have shown that definitely 
alkaline peroxide solutions will oxidize sodium thiosulfate com- 
pletely to sulfate and the study of alkalies in hypo elimination has 
shown that ammonia is the most suitable alkali for this purpose. It 
has the additional advantage that it is volatile, so that, after treat- 
ment, the only residue is a trace of sodium and ammonium sulfates. 
An investigation was therefore made of ammonia-peroxide solutions 
to determine their activity in the elimination of hypo from prints. 

At the outset, mixtures of peroxide with increasing concentrations 
of ammonia were prepared to determine the pH range of the solution 
over which effective oxidation of hypo was attained (Table II). 



Nov., 1940] ELIMINATION OF HYPO FROM IMAGES 495 

Solutions having a H value lower than 9.8 were not entirely satis- 
factory as hypo eliminators because of their low activity. The three 
solutions containing 500, 250, and 125 cubic-centimeters of 3 per cent 
peroxide per liter with 10 cubic-centimeters of 28 per cent ammonia in 
each were compared throughout the study. Dilutions with water 
of any of these solutions produced mixtures which would not ef- 
ficiently remove the last traces of sodium thiosulfate. Table III 
illustrates typical results obtained by treatment in these solutions 
for different times after increasing times of washing. 

TABLE m 

The Elimination of Hypo from Double-Weight Prints with Per oxide- Ammonia 

Time of Time of 

Peroxide-Ammonia Washing Treatment Hypo Concentration 

(Cc per Liter) (Min) (Min) (Mg per Sq-In) 

500 +10 10 5 0.040 

(Peroxide) (Ammonia) 10 0.006 

3% 28% 15 Nil 

20 5 0.004 

10 Nil 

30 5 0.004 

10 Nil 

250 +10 10 5 0.038 

(Peroxide) (Ammonia) 10 0.007 

3% 28% 15 Nil 

20 5 0.008 

10' Nil 

30 5 0.007 

10 Nil 

125 +10 10 5 0.055 

(Peroxide) (Ammonia) 10 0.007 

3% 28% 15 Nil 

20 5 0.006 

10 Nil 

30 5 0.005 

10 Nil 



It is apparent from Table III that, if double-weight prints are 
washed for 20 minutes and then bathed for 10 minutes in the elimina- 
tor solution, the hypo is completely eliminated from the prints in 
the case of all three of the above solutions containing varying quan- 
tities of peroxide. The disadvantage of the 125/10 peroxide-am- 
monia mixture is its shorter exhaustion life as compared with the 



496 CRABTREE, EATON, AND MUEHLER [j. s. M. P. E. 

500/10 mixture. For single- weight prints, a shorter wash will suf- 
fice. All prints must be washed for at least 5 to 10 minutes after the 
eliminator treatment. 

A duplicate set of the prints shown in Fig. 4 was treated in a 
hydrogen peroxide solution for 5 minutes, washed for 5 minutes, and 
then subjected to the accelerated fading test at the same time as the 











FIG. 5. Accelerated fading tests illustrating the effectiveness of the peroxide- 
ammonia hypo eliminator. The upper row of prints contained quantities of 
hypo designated in milligrams per square-inch and did not receive elimina- 
tor treatment. The lower row of prints contained same quantities of hypo 
and were treated 5 minutes in an eliminator solution consisting of 500 cc of 
3 per cent hydrogen peroxide and 10 cc of 28 per cent ammonia per liter. 
They were then subjected to the same accelerated fading conditions. Note 
absence of fading. 



prints which were not treated in the eliminator solution. The effect 
of the peroxide-ammonia eliminator in preventing fading is illustrated 
in Fig. 5. 

An extensive study of the application of these solutions in the 
photographic trade was made with special attention to exhaustion 
life of the solutions, and to any possible deleterious effects in com- 
mercial processing. The specific application is dependent upon the 
use intended. At the outset, since it is never possible to predict the 



Nov., 1940] ELIMINATION OF HYPO FROM IMAGES 497 

conditions to which a print may be subjected, every photographer 
must eliminate the hypo completely from prints and negatives, even 
if this may require some slight modification of his processing machine 
or the method of working. 

PRACTICAL RECOMMENDATIONS 

With negatives and transparencies or, in general, any gelatin 
silver image on a waterproof support, if, during washing an adequate 
renewal of the wash water prevails, the hypo can be removed com- 
pletely by water alone in a reasonable time at a temperature of 60 
to 70F without the use of a hypo eliminator. 

If it is necessary to speed up the processing by using a shorter 
washing time, a supplementary alkaline bath may be used. After 
the negatives have been washed for 10 minutes, they should be 
bathed in an 0.3 per cent solution of ammonium hydroxide (100 
cubic-centimeters of 28% ammonia per liter) for 3 minutes and then 
washed for 2 or 3 minutes. 

The rate of washing is also hastened if a chrome alum or nonhard- 
ening fixing bath is employed. 

With photographic prints, washing is hastened by using water at 
around 70F, but it is never possible to remove the hypo completely 
by merely washing so that the print will not subsequently fade if sub- 
jected to abnormal conditions of temperature and humidity. The 
use of the following peroxide-ammonia eliminator is necessary to 
insure permanency: 

KODAK HE-l 

Hypo Eliminator Solution for Professional and Amateur Use 

Avoirdupois Metric 

Water 16 ounces 500. Occ 

Hydrogen Peroxide (3% solution) 4 fluid oz 125.0 cc 

Kodak Ammonia (3% solution) 3 : /4 fluid oz 100.0 cc 

Water to make 32 ounces 1 . liter 

To make 3 per cent ammonia, dilute 1 part of 28 per cent ammonia with nine 
parts of water. 

Directions for Use. Wash the prints for about 30 minutes at 65 to 70 F* 
in running water which flows rapidly enough to replace the water in the vessel 



* For lower temperatures, increase the washing time. Double the washing 
time should be used when double-weight prints are treated. 



498 CRABTREE, EATON, AND MUEHLER [j. s. M. p. E. 

(tray or tank) completely once every 5 minutes. Then immerse each print 
about 6 minutes at 70 F in the Hypo Eliminator Solution (Kodak HE-1), and 
finally wash about 10 minutes before drying. 

Life of Kodak HE-1 Solution. About fifty 8-inch X 10-inch prints or their 
equivalent per gallon (4 liters). 

Test for Hypo. Process with the batch of prints, an unexposed white sheet of 
photographic paper (same weight and size as majority of prints in batch). After 
the final wash, cut off a strip of this sheet and immerse it in a 1 per cent silver 
nitrate solution for about 3 minutes; then rinse in water and compare, while wet 
in subdued daylight or artificial light, with the wet, untreated portion. If the 
hypo has been completely removed, no color difference should be observed. 
A yellow-brown tint indicates the presence of hypo.* Caution: Silver nitrate 
solution stains the skin black; avoid direct contact with the solution. 

* A positive test with silver nitrate may also be obtained in the absence of 
hypo, if hydrogen sulfide or wood extracts are present in the water supply. 

KODAK HE-2 

Hypo Eliminator Solution for Commercial Photofinishing Use 

Avoirdupois Metric 

Water 10 ounces 300. Occ 

Hydrogen Peroxide (3% solution) 16 ounces 500. Occ 

Kodak Ammonia (3% solution) 3 l / 4 ounces 100. Occ 

Water to make 32 ounces 1 . liter 

To make 3 per cent ammonia, dilute 1 part of 28 per cent ammonia with nine 
parts of water. 

Directions for Use. Wash the prints about 15 minutes at 65 to 70 F* in 
running water which flows rapidly enough to replace the water in the washing 
vessel (tray or tank) completely once every 5 minutes. Then immerse each 
print for about 5 minutes in the Hypo Eliminator Solution (Kodak HE-2), and 
finally wash about 10 minutes before drying. 

When using a Pako Print machine (or similar equipment), replace the water 
in the second wash tank with the Hypo Eliminator Solution (Kodak HE-2), and 
process the prints as usual. 

Life of Kodak HE-2 Solution. About eighty 8-inch X 10-inch prints or their 
equivalent per gallon (4 liters). 

Test for Hypo. Use the same test as recommended for use with Kodak HE-1 
Solution. 



* For lower temperatures, increase the washing time. Double the washing 
time should be used when double-weight prints are treated. 

The above treatment will insure the absence of fading from internal 
fading agents. However, a hypo-free image will be attacked by hy- 
drogen sulfide which is present in the products of combustion of 



Nov., 1940] ELIMINATION OF HYPO FROM IMAGES 499 

coal gas and in the atmosphere of industrial regions. This external 
fading is accelerated by the presence of acidic gases and by high 
temperature and high humidity. 

The use of water-miscible (paste) adhesives for mounting also con- 
tributes to fading, since such adhesives are usually hygroscopic and 
the resulting moist condition of the print is favorable to more rapid 
chemical reaction. 

Fading due to external agents may be minimized by (1) the use of 
a waterproofing lacquer over the print surface, (2) the use of Dry 
Mounting Tissue, and (3) bathing the print in a solution of a salt of 
a noble metal, such as gold chloride (with sodium thiocyanate), 
when the metal ion displaces the outer layer of the silver grains, 
usually with a negligible change in image color. A suitable formula 
consists of gold chloride, 0.1 gram; sodium thiocyanate, 10 grams; 
dissolved in 1 liter of water. 

It is essential that the solution be prepared just before use and 
in the following manner: Add 10 cubic-centimeters of a 1-per cent 
gold solution to a 1 -liter vessel and dilute to approximately 700 
cubic-centimeters. Dissolve the thiocyanate in a small volume of 
distilled water and add slowly to the gold solution with continuous 
agitation. Then make up to 1 liter with water. 

Bathe either the freshly washed or dried prints for 8 minutes at 
70 to 75F with agitation or until a just perceptible change in tone 
occurs and then wash for 5 minutes before drying. The life of the 
bath if used immediately is approximately thirty 8-inch X 10-inch 
prints per gallon of solution. 

The gold treatment also stabilizes the image against fading by 
hypo. It is not quite as effective, however, as the peroxide-ammonia 
treatment and has the disadvantage that the color of the image is 
changed slightly. 

With respect to fading by hydrogen sulfide, lacquering the print 
surface is helpful but not as effective as the gold treatment. Dry 
mounting in combination with a lacquer is surprisingly effective, from 
which it is apparent that the hydrogen sulfide attacks the image 
appreciably from the rear through the paper stock as well as at the 
surface. 

A combination of these procedures, namely, (1) use of the peroxide- 
ammonia hypo eliminator, (2) treatment with the gold solution, (3) 
the use of Dry Mounting Tissue, and (4) lacquering of the print 
surface, will insure maximum permanency of the gelatin silver print 



500 CRABTREE, EATON, AND MUEHLER \j. s. M. P. E. 

image. Conversion of the silver image to silver sulfide by sulfide 
toning in the usual manner, or to silver selenide or telluride, will also 
insure maximum permanency, although such treatments change the 
color of the image. 

OCCASIONAL EFFECTS WHEN USING THE PEROXIDE-AMMONIA TREATMENTS 

HE-1 AND HE-2 

(1) A slight change in tone: This tone change is not as great 
as that produced by ferrotyping and, therefore, is considered to be 
negligible for glossy papers. When it is desired to prevent the slight 
tone change on professional papers, 15 grains of potassium bromide 
should be added to each quart (1 gram per liter) of the Kodak HE-1 
bath. 

(2) A slight yellowing of the whites (undetectable on buff papers) : 
To minimize this effect, the prints should be bathed in either a 1- 
per cent acetic acid solution or a 1 per cent sodium sulfite solution for 
about 2 minutes immediately after treatment in HE-1 or HE-2 and 
prior to the final wash. 

(3) If the prints feel too slippery after the eliminator, they should 
be immersed for 1 minute in a 1-per cent solution of acetic acid and 
then washed for 3 or 4 minutes. 

(4) A slight tendency for treated prints to stick to a hot belt 
dryer. To prevent this, the prints should be bathed, prior to drying, 
for 3 to 5 minutes in a 50-per cent denatured alcohol solution. A 
2-per cent potassium alum solution is effective but requires a rinse of 
several minutes in water after the treatment. 

(5) An occasional tendency for treated glossy prints to ride the 
squeegee roll of the ferrotype dryer (especially prints which have 
been accidentally fed into the machine emulsion side up), or to stick 
to the chromium drum itself. To overcome these difficulties, the 
prints should be bathed for 2 minutes in a 50-per cent denatured 
alcohol solution just prior to ferrotyping. 

(6) While cleanliness of the drum surface is essential for the 
satisfactory ferrotyping of all prints, it is especially important as a 
sticking preventative in the case of peroxide-ammonia treated prints. 
Excessive drum temperatures should also be avoided. 

RELATION BETWEEN THE THEORETICAL AND PRACTICAL QUANTITIES OF HYPO 
REQUIRED TO PRODUCE FADING 

It is of interest to study the relationship between the theoretical 
quantity of sodium thiosulfate required to convert any given silver 



Nov., 1940] ELIMINATION OF HYPO FROM IMAGES 501 

image to silver sulfide and the quantities actually required to produce 
fading under accelerated conditions in practice. 

The "photometric equivalent" 12 may be defined as the number of 
grams of silver in a 100 square-centimeter area of emulsion which are 
necessary to give a density of 1.00. Its magnitude varies with the 
exposure, the degree of development, and the grain size of the emul- 
sion, ranging from approximately 0.005 to 0.035, depending upon the 
type of the emulsion. 

Hickman and Spencer 13 calculated the quantity of thiosulfate re- 
quired to react with the silver in an image having a density of 0.10 
and made the assumption that only one-tenth of the silver need be 
sulfided to produce just visible fading, which seems reasonable. The 
reaction may be expressed by the equation 

2Ag+ + So0 3 > Ag 2 S + S0 3 

Silver Thiosulfate Silver 

Ion Sulfide 

To express the quantity of thiosulfate in milligrams per square-inch 
which is required to fade an image of density 0.10, the following 
formula was employed : 

Molecular Weight 
Photometric of Sodium Thiosulfate Conversion Factor 



v ir)C w v ni 

Equivalent 2X Atomic Weight Metric to Avoir. 

of Silver 



The sulfiding reaction first occurs visibly in the low densities having 
a value of approximately 0.10. The photometric equivalents at low 
densities are given in Table IV and also the theoretical quantity of 
thiosulfate required to produce fading at a density of 0.10. In- 
cluded in the same table are limiting concentrations of hypo above 
which fading occurred under the conditions of the accelerated fading 
test. 

In general, the faded images with the intermediate and high-speed 
materials possessed a purplish-black coloration not greatly different 
in appearance from the original and often of similar printing density. 
The images of motion picture positive emulsions became more yellow- 
ish-brown than those of the high-speed materials but only when the 
hypo content was in considerable excess of 0.07 milligram per square- 
inch. With the finest-grained materials, a definite yellowing occurred 
at concentrations of thiosulfate greater than 0.02 milligram per square- 
inch. 



502 



CRABTREE, EATON, AND MUEHLER [j. s. M. p. E. 



A comparison of the theoretical values given in Table IV with the 
quantities determined by experiment reveals that (7) with chloride 
paper emulsions the hypo content should not exceed 0.002 to 0.005 
milligram per square-inch or 0.02 milligram per square-inch with 
chlorobromide emulsions; (2) with film emulsions, in general, more 
hypo is allowable than the calculated theoretical value, for example, 
(a) fine-grain materials 2 to 3 times, and (b) with negative materials, 
4 to 9 times. This indicates that when a safety factor of 10 is assumed 
in the determination of the quantities of hypo required to fade images, 
in general, the formula is applicable only to paper emulsions. With 
film emulsions, it is apparently necessary to convert from 25 to 50 
per cent of the total mass of the image to silver sulfide before the 
image color changes appreciably. 



TABLE IV 



Material 

Chloride paper emul- 
sions 
Chlorobromide paper 

emulsions f 
Fine grain lantern 

slide 14 

Fine grain emulsion 
Process emulsion 16 
Process emulsion 16 
Commercial emulsion 16 



Density 

at Which 

Photometric 

Equivalent 

Was 
Measured 



0.25 
0.08 
1.00 

0.47 
0.13 
0.09 
0.13 
0.56 



Photometric 
Equivalent 

at 

Indicated 
Density 



0.0087 

0.009 

0.005 

0.0108 
0.0153 
0.0235 
0.0226 
0.0228 



Calculated 
Quantity 
of Hypo 
(Mg per Sq-In) Concentration 
Required of Hypo 
to Cause Required 
Fading at in Practice* 
Density of 0.1 (Mg per Sq-In) 


0.005** 0.002-0.005 


0.007 
0.007 


0.02 


0.008 






0.02 


0.008^ 




0.011 
0.018 


0.07 


0.017 ' 
0.017 


0.14 



* These figures represent average values for the types of materials mentioned. 
** Chloride emulsions are more fine-grained than chlorobromide emulsions 
and the photometric equivalent is probably as low as 0.005. 

f Unpublished results S. E. Sheppard and A. Ballard, Kodak Research 
Laboratories. 

All the types of emulsions mentioned are readily washed to the 
degree indicated in Table IV and, in good commercial practice, are 
usually washed to concentrations well below those given. Process, 
motion picture positive, and fine-grain emulsions, for example, often 
contain as little as 0.005 milligram per square-inch, as determined by 
the Crabtree-Ross method. This method of analysis has been 
adopted by the National Bureau of Standards. 16 



Nov., 1940] ELIMINATION OF HYPO FROM IMAGES 503 

ACKNOWLEDGMENT 

The authors are greatly indebted to Mr. Milton F. Fillius and Mr. 
Peter Hass of the Paper Service Department of the Eastman Kodak 
Company for assistance in the experimental work. 

REFERENCES 

1 CRABTREE, J. I., AND Ross, J. F.: "A Method of Testing for the Presence 
of Thiosulfate in Motion Picture Film," /. Soc. Mot. Pict. Eng., XIV (1930), 
p. 419. 

2 LUMIERE, A. & L., AND SsYEWETZ, A. : "Ammonium Thiosulfate as a Fixing 
Bath," Brit. J. Phot., 55 (1908), p. 417. 

3 WEYDE, E.: "On the Possibility of Improving the Permanence of Photo- 
graphic Prints," Photo Woche, 25 (1935), p. 474. See also Brit. J. Phot., 82 
(1935), p. 376, and Veroff. wiss. Zentral-Lab. phot. Abt. Agfa, V (1937), p. 181. 

4 "Reducible Sulfur in Paper," Paper Trade J., Tech. Assoc., Sec. 108 (March 
2, 1939), p. 24. 

6 CRABTREE, J. I., AND Ross, J. F.: "A Method of Testing for the Presence 
of Thiosulfate in Motion Picture Film," J. Soc. Mot. Pict. Eng., XTV (1930), 
p. 419. 

6 LUMIERE, A. AND L., AND SEYEWETZ, A.: "Entfernung des fixiernatrons 
durch Waschen mit Wasser," Eder's Jahrbuch (1908), p. 505. 

7 HAUBERRISSER, G.: "tiber das Entfernen von Fixiernatron aus photo- 
graphischen Schlichten durch Auswassern bei Hoherer Temperatur," Phot. Rund., 
24 (1910), p. 91. 

8 HART, F. W.: "Early History of Hypo Eliminators," Brit. J. Phot., 35 
(1888), p. 151. 

9 SMITH, A.: "On the Removal of the Last Traces of Hyposulfites from Posi- 
tive Paper Prints," Brit. J. Phot., 13 (May, 1866), p. 226. 

10 SPILLER, J.: "Photography in Its Chemical Aspects," Phot. J., 11 (June, 
1866), p. 16. 

11 Footnote, Das Lichtbild, 7 (1931), p. 42. 

12 SHEPPARD, S. E., AND BALLARD, A.: "The Covering Power of Photographic 
Silver Deposits I," J. Frank. Inst., 206 (1928), p. 659. 

13 HICKMAN, K. C. D., AND SPENCER, D. A.: "The Washing of Photographic 
Products," Phot. J., 62 (1922), p. 225. 

14 EDER, J. M. : "Structure and Composition of Silver Bromide Gelatin Plates, 
Films, and Developing Papers," Camera (Luzern), 4 (1925-26), p. 29. 

15 SHEPPARD, S. E., AND BALLARD, A.: "The Covering Power of Photographic 
Silver Deposits I," /. Frank. Inst., 206 (1928), p. 135. 

16 "Evaluation of Motion Picture Film for Permanent Records," Misc. Pub. 
M-158, U. S. Dept. of Comm., National Bureau of Standards (1937), p. 5. 

CHRONOLOGICAL HISTORY OF HYPO ELIMINATORS 

1855. Alum: "On Positive Printing," by J. Newton (/. Phot. Soc., 31, June 
1855, p. 176) "... immerse in hyposulfite for about 2 or 3 minutes, then 



504 CRABTREE, EATON, AND MUEHLER [j. s. M. P. E. 

in alum water for half an hour and change the water entirely two or three 
times." 

1855. Caustic Potash: "Communication on Positive Photographs," by Mr. 
Malone (/. Phot, Soc., 31, June 1855, p. 177) "I suggest that you should 
treat the positive photograph, fixed in the ordinary way, with a strong 
solution of caustic potash heated to about 180 Fahrenheit; . . . carefully 
washing out the potash." 

1856. Dilute Alkali or Alkaline Carbonate: "Photographic Chemistry," by F. 
Hardwick, Churchill, London (3rd Ed., 1856, p. 170). ". . . and the 
removal of the size which can be effected by means of a dilute alkali or 
an alkaline carbonate, . . . has the additional advantage of carrying out 
the last traces of hyposulfite of soda. . . ." 

1864. Hypochlorous Acid: "Minutes of Meeting of South London Photographic 
Society," by F. W. Hart (Brit. J. Phot , 11, March, 1864, p. 82). Sug- 
gested the use of chlorine and barium chloride in aqueous solution to 
convert hypo to barium sulfate and sodium chloride. 

1866. Hydrogen Peroxide: "On the Removal of the Last Traces of Hyposulfites 
from Positive Paper Prints," by A. Smith (Brit. J. Phot., 13, May, 1866, 
p. 226). Recommended the use of hydrogen peroxide, diluted with one 
thousand times its volume of water, for one or two minutes. Advised 
the neutralization of the acid in the peroxide with soda. The treatment 
required a rinse in water as the final operation. 

1866. Hydrogen Peroxide and Ammonia: "Photography in Its Chemical 
Aspects," by J. Spiller (Phot. J., 11, June 1866, p. 58). Used hydrogen 
peroxide with ammonia but claimed that the two were "mutually de- 
composed." Then suggested treating first in hydrogen peroxide followed 
by ammonia. Note: A discussion of this paper, reported in Brit. J. 
Phot., 13, 1866, p. 283, recommended treating the prints first hi ammonia 
and then in hydrogen peroxide. 

1866. Sodium Hypochlorite: "On the Elimination of the Double Hyposulfites 
of Soda and Silver from Photographic Prints," by F. W. Hart (Brit. J. 
Phot., 13, June, 1866, p. 290). Recommended sodium hypochlorite 
followed by very dilute ammonia to dissolve traces of silver chloride. 

1866. Chloric and Perchloric Acids: Editorial "Permanent Prints: A New 
Plan," by Messrs. Tichborne and Robinson (Brit. J. Phot., 13, Dec., 
1866, p. 580). Twenty-four grains of barium chlorate are dissolved hi 
one ounce of water and 20 minims of 12 per cent perchloric acid added. 
For use add 2 ounces of this solution to one pint of hot water. Treat 
prints for about an hour and wash in water. 

1872. Iodine: "The Chemistry of Photography," by W. Harrison (Scovill and 
Adams Co., New York, N. Y., 1892, p. 412). Vogel is credited with the 
first use of iodine. After careful washing the prints were placed in water 
to which enough iodine solution was added to give it a sherry color; then 
rinsed in a very weak solution of sulfite and sodium carbonate to remove 
the blue color and finally washed in water. 

1881. Alum: "Notizen zum Bromsilber Gelatine Verfahren," by J. M. Eder 
(Phot. Korr., 18, 1881, p. 203). Used a saturated solution of alum 
diluted one to ten with water. 



Nov., 1940] ELIMINATION OF HYPO FROM IMAGES 505 

1881. Zinc Hypochlorite: L. Belitzski and G. Scolik (Eder's HandbuchPartlll, 
Knapp, Halle (4th Ed.), 1890, p. 317). Used in dilute water solution. 
Known as Flandreaus' eliminator in America. 

1883. Bromine Water, Etc.: "Die Beseitigung des unter schwesligsauren 
Natrons," by F. Stolze (Phot. Wochenblatt, 1883, p. 348). Javelle water, 
hydrogen peroxide, iodine water, bromine water, lead nitrate, and barium 
nitrate are discussed. Alum with citric acid in water was suggested. 
Successive five-minute treatments were used and the wash water tested 
after each wash. None of these was considered entirely satisfactory. 

1888. Hypo Eliminator: "Early History of Hypo Eliminators," by F. W. Hart 
(Brit. J. Phot., 35, 1888, p. 151). The claim to the original use of the 
term "hypo eliminator" is made. 

1889. Sodium Chloride: Editorial (Amer. Phot., 19, 1899, p. 38). Reference 
to the use of sodium chloride as an eliminator by Dr. Bannon but no 
directions are given. 

1894. Potassium Persulfate: Mention of its use by Schering is made by L. P. 
Clerc in his book "Photography Theory and Practice," Pitman, London, 
1930, p. 269. 

1897. lodated Salt: "Sel lode Eliminateur Rapide des Hyposulfites," by M. P. 
Mercier (Bull, de la Soc. FranQ. de Phot., 30, 1897, p. 296). A suggested 
formula was iodine 3 parts, salt 30 parts, and sodium carbonate 30 parts 
dissolved in 1000 parts of water. "Decolorize with ammonia just before 
use. The print may be left in this solution for a long time because the 
colorless solution does not attack the silver image. Iodine or iodides 
may be used with alkali or alkali salts and bromine or bromides may be 
used but the latter are much slower acting." 

1901. Potassium Percarbonate: Use by G. Meyer is mentioned by L. P. Clerc 
hi his book "Photography Theory and Practice," Pitman, London, 
1930, p. 269. No directions are given. 

1902. Ammonium Persulfate: "Use of Various Oxidizers for the Destruction 
of Hypo," by A. and L. Lumiere and A. Seyewetz (Bull, de la Soc. Prang, 
de Phot., 10, 1902, p. 270). Hydrogen peroxide, potassium percarbonate, 
and commercial ammonium persulfate were the best hypo oxidizers but 
ammonium persulfate was the most practical provided the free acid was 
first neutralized with either carbonate, bicarbonate, alkaline phosphates, 
alkaline citrates, alkaline tungstate, or borax. Low concentrations were 
satisfactory. 

1903. Alkaline Perborates: G. F. Jaubert. Mentioned by L. P. Clerc in his 
book "Photography Theory and Practice," Pitman, London, 1930, p. 
269. No directions given. 

1903. Sodium Chloride: O. Baysellance (Phot. Rev., 12, July 26, 1903, p. 32). 
"Treat 1 /2 to one hour in 3-per cent sodium chloride and then give three 
or four rinses in water." 

1904. Potassium Permanganate: "Permanganate as an Eliminator of Hypo," 
by I. Pearse (/. Phot. Soc. India, 1904; Cf. Photography, 20, 1905, p. 197). 
Use water slightly colored with permanganate and use successive solu- 
tions until no change hi color occurs. Less than ten minutes of this 
treatment was equal to two hours washing. 



506 CRABTREE, EATON, AND MUEHLER 

1912. Bisulfite-Formaldehyde: "A Hypo Remover," by E. D. Davison ( Camera 
Craft 19, 1912, p. 30). Recommended water 40 parts, sodium bisulfite 
3 parts, and formaldehyde 8 parts. Treat prints (after washing) for 
10 to 15 minutes in a solution diluted 1 : 3 with water. 

1922. Chloramine T (Sodium p-toluene Sulf ochloramide) : "A New Quick 
Clean Eliminator of Hypo," by E. F. Shelberg (Amer. Phot., 16, April, 
1922, p. 267). Dissolve one tablet in 40 oz water and treat for two or 
three minutes, washing before drying, 

1923. Dilute Sodium Carbonate: Unpublished data on the use of alkalies in 
hypo eliminator by F. J. Norton and J. I. Crabtree (Kodak Research 
Laboratories) July- August, 1923. Dilute solutions of sodium carbonate 
were recommended for use immediately after fixing. 

1923. Alkali Carbonate or Phosphate: "Adsorption of Sodium Thiosulfate by 
Photographic Paper," by A. Charriou (Compt. Rend., 177, 1923, p. 482). 
Claimed that hypo was displaced more readily by washing in a solution 
of alkali carbonate or phosphate than by water. 

1925. Ferrous Sulfate: "Hypo Eliminators and Intensifies." Brit. Pat. 
225,664, Oct. 9, 1923 ( Brit. J. Phot., 72, 1925, p. 24) . Three parts ferrous 
sulfate and one part sodium chloride were thoroughly mixed. Prints 
were treated in a solution containing 8 grains of this mixture in l*/2 pints 
of water and washed before drying. 

1925. Sodium Hydroxide: "Hypo Eliminator," by A. E. Amor (Brit. J. Phot., 
72, 1925, p. 18). Claimed that 0.2 per cent sodium hydroxide and a 
persulfate formula of the following composition were most effective elimi- 
nators but neither was an improvement over careful washing: Persulfate 
6 grams, sodium carbonate 12 grams, water 1000 cubic-centimeters. 

1931. Sodium Hypochlorite Plus Sodium Chloride: R. Namias (II prog, fot., 38, 
1931, p. 125). This combination was an improvement over hypochlorite 
alone. Negatives were washed five minutes, treated in 0.3 per cent sodium 
hypochlorite plus 1 per cent sodium chloride solution and washed for one 
or two minutes. 

1931. Hydrogen Peroxide Plus Ammonia: Note in Das Lichtbild, 7, 1931, p. 42. 
Ammonia was added drop wise until the solution just smelled of ammonia. 

1932. Dilute Caustic Soda: "The Use of Alkalies as Hypo Eliminators," by 
E. E. JeUey (Phot. J., 72, 1932, p. 480). Kodak Research Laboratories 
Communication No. 503H. 

1937. Sodium Carbonate 1 %: "On the Possibility of Improving the Perma- 
nence of Photographic Prints," by E. Weyde (Veroff. wiss. Zentral-Lab. 
phot. Abt. Agfa, V, 1937, p. 181). Also, Brit. J. Phot., 82, 376, June 14, 
1935, p. 376, and Photo Woche, 25, 1935, p. 474. For best hypo elimina- 
tion the use of a nonhardening fixing bath followed by bathing in 1 per 
cent sodium carbonate before washing was recommended. 



NEW MOTION PICTURE APPARATUS 

During the Conventions of the Society, symposiums on new motion picture appara- 
tus are held, in which various manufacturers of equipment describe and demonstrate 
their new products and developments. Some of this equipment is described in the 
following pages; the remainder will be published in subsequent issues of the Journal. 



A NEW RECORDING MACHINE COMBINING DISK RECORDING AND 

MAGNETIC RECORDING, WITH SHORT REFERENCE TO 

THE PRESENT STATUS OF EACH* 

S. J. BEGUN** 

Although there seems to be no doubt that sound-on-film will retain its pre- 
dominant position in the screen entertainment field, on the other hand, there can 
be no question that the talking motion picture will also be used more and more 
in the home entertainment field; and recording methods other than optical may 
prove superior and better adapted to this application. Furthermore, for many 
years, disk recording has been used in the recording studio to give the recording 
engineer an opportunity to check the quality of the recording without having to 
wait for the development of the film. In certain cases, even re-recordings have 
been made from disk to the film, and there frequently may be occasions where 
re-recording from one recording medium to the other may be quite recommendable. 
By using the method of re-recording more frequently, film material may in many 
cases be saved, and the considerable expense for film that now has to be thrown 
away may be considerably reduced, particularly if the other recording materials 
are cheaper per unit tune than the film. 

It seems timely, therefore, to discuss two methods of recording other than the 
sound-on-film process, with which the sound-film engineer is so familiar. These 
two methods are disk recording and magnetic recording. As a result of consider- 
able work that has been done on these two methods in the past few years, they 
are both capable of really high-fidelity reproduction of a signal. 

DISK RECORDING 

So far as disk recording is concerned, recording and reproducing a frequency 
range flat up to 10,000 cycles with negligible distortion is more than a theoretical 
ideal it is a proved possibility. Listeners, including sound engineers, who have 
heard such recordings played in conjunction with an excellent sound system have 
remarked upon the brilliancy and cleanness of reproduction now obtainable. 
While the writer is quite aware of the good results to be obtained with studio film 

* Presented at a Meeting of the Atlantic Coast Section, April 17, 1940. 
** Brush Development Co., Cleveland, Ohio. 

507 



508 NEW MOTION PICTURE APPARATUS tf. S. M. p. E. 

recordings, he dares to say that the present high-fidelity disk recordings are, in 
every way, equal to, if not better than, the best that has so far been accomplished 
with film recording. 

With professional disk recording equipment very good results have been ob- 
tained for the last few years. But such professional equipment has been quite 
expensive. The best proof of the considerable progress in the disk recording 
field is the fact that home recording units, even in the low-price range, will soon 
be available. These units will have a quality of performance comparable to that 
of radio chain programs. This progress has been possible only because the 
development laboratories have been busy investigating the important factors 
controlling the quality of recording, and analyzing the problems that for many 
years have been neglected. 

Disk recording, or as it should be called, mechanical recording, can look back 
upon a history of almost sixty years. Only lately, however, have the engineers 
been able to improve the various components in the recording and reproducing 
chain to such an extent that really high-fidelity performance can be obtained. 

A disk recording unit consists of four essential parts the turntable, the disk 
cutting device, the disk material, and the reproducer. Microphone, amplifier, 
and loud speaker are also parts of the complete system, but they will not be 
discussed in detail in this paper. 

The Turntable. The turntable includes the motor, with its drive for the turn- 
table proper, and the feed mechanism for moving the motor along a radius of 
the disk from the inside outwardly or vice versa. It is well known that during 
the recording and playback process, constancy of speed is an essential factor 
for any recording device. In general, two kinds of speed variations can be dis- 
tinguished: one causes a slow periodic change of speed, the other, a fast periodic 
change of speed. The low-frequency speed changes are evidenced by a waver 
known to the profession as "wow," and which is particularly objectionable in 
long, sustained notes. The higher-frequency speed changes, on the other hand, 
may not be noticeable to the ear as such, but will cause distortions of an objec- 
tionable character. An otherwise clean sinusoidal tone, when reproduced by a 
system having this high-frequency flutter, will sound badly distorted. 

Furthermore, a turntable should be as free from mechanical vibration as pos- 
sible. Since the recording and reproducing process is essentially a mechanical 
process, such mechanical vibration, being of the same nature as the recorded sig- 
nal, will produce, during the playback, a signal pick-up technically described as 
"rumble." The intensity of these vibrations, in the case of a poor turntable, may 
be so great as actually to overload the playback amplifier, producing distortion 
and cross-modulation of the useful signal. 

Producing a satisfactory turntable is much more of a problem than it seems at 
first glance. There are in general two methods of building a turntable in order 
to approach the requirements of a flutter-free and rumble-free drive. One method 
is to use what may be called a "brute force" design. This involves a very massive 
turntable and a comparatively small driving force, coupled flexibly one to an- 
other. 

A very satisfactory example of this method is the use of a string drive coupling 
a synchronous motor to such a heavy turntable. Fig. 1 shows the principal parts 
of such a design. A turntable drive built after this fashion is in use in these 



Nov., 1940] 



NEW MOTION PICTURE APPARATUS 



509 



laboratories and performs very satisfactorily. It is advisable in discussing the 
design principles of such a turntable to emphasize the fact that the driving motor 
must have sufficient power, with some reserve to provide the necessary torque. 
On the other hand, however, the motor should not be so powerful that its un- 
avoidable speed variations are delivered in sufficient force to influence the smooth 
rotation of the turntable. In this connection, it should be pointed out that even 
synchronous motors are not entirely free of speed variations. Even though these 
motors turn, on the average, in accurate synchronism with the supply frequency, 
during a revolution the armature may not always move with constant angular 
velocity, and may "hunt" considerably about a mean average speed. 

If "brute force" filtering is not used, it is necessary to incorporate a filter as 
part of the transmission member between the motor and the turntable. This 
is usually done by providing a low-pass mechanical filter, using one or more 
stages of inertia and stiffness members. Some of these filters are rather com- 




To n>f> or *torae. 



FIG. 1. String-driven turntable. 



plicated, but the most prevalent today, which is apparently reasonably satis- 
factory (at least for the home recording field) , is the turntable rim drive. 

Such a drive is shown in Fig. 2. It consists of a motor engaging the rim of the 
turntable by means of a rubber pulley. In this case, the mass of the filter is 
represented by the turntable and the armature of the motor, and the stiffness 
is provided by the resilience of the rubber pulley. 

There are several variations of the rim drive. One is provided by covering the 
inside rim of the turntable with a rubber tire which is engaged by the metallic 
motor pulley; another is provided by an intermediate rubber wheel which engages 
a metallic motor shaft on one part of its circumference, and a metallic turntable 
rim on another part. Some of these rim-driven turntables are surprisingly free 
from flutter, and such designs seem very promising. The simplicity of the rim- 
driven turntable will undoubtedly popularize it, particularly in the low-price 
field. In addition, relatively inexpensive provisions can be made for changing 
the turntable speed from 78 to SSVs rpm. 

There are also turntables incorporating gear trains. Some of these turn- 
tables give very satisfactory results, but require very carefully machined gears, 
and are therefore extremely expensive. Some other turntables of this kind, how- 



510 NEW MOTION PICTURE APPARATUS [J. S. M. p. E. 

ever, are inferior, as insufficient care is taken in their engineering. If a turntable 
of this class is to be used, extreme care must be given to the selection of proper 
equipment. 

The Feed Mechanism. Regarding the feed mechanism, any such device will 
be satisfactory if it has no backlash and provides a smooth progression across the 
radius of the disk, either inside out or vice versa. Preferable are those feed 
mechanisms that move the cutter along a diameter across the disk, thus providing 
regular groove spacing with no tracking error. Any high-fidelity instrument 
should be equipped with a feed mechanism of this design characteristic. So far 
as the less expensive recording turntables are concerned, the feed mechanism 
must be simple and inexpensive. In this case, the cutter may be held in an arm 
like a pick-up, and moved in an arc. By offsetting the cutting head on such an 
arm, the tracking error can be greatly reduced to the point where it is no longer 
a serious problem. 



HM.I&- (o*/r*crs /fMex su&Acf of 

PI TtJKHTA&Lf 




FIG. 2. Rim-driven turntable. 

An arm moving in an arc may be coupled to the turntable or may be driven 
independently. In either case, feed mechanisms have been built of sufficiently 
good accuracy for most ordinary work. One of the most common feed mecha- 
nisms used in lower-priced recorders is illustrated hi Fig. 3. 

The independently driven feed mechanism may have the advantage of greater 
flexibility. This makes it possible to change the spacing between the grooves 
over a wide range without necessitating a change in the ratio of reduction of the 
gearing arrangement. This change would be necessary in the case of a direct 
drive on the turntable. 

Cutting Head. The next important component in the recording system is the 
cutting device, generally referred to as the cutter or cutting head. The prin- 
cipal requirement of the cutter is to cut a mechanical facsimile of a given sound- 
wave into the recording material. To do this, the cutter must be quite inde- 
pendent of any load imposed by the cutting medium. This is required par- 
ticularly because of the fact that the load imposed by the cutting medium may 
vary not only with the depth of cut, but also with different mediums. To provide 
a sufficient reserve of force in the cutting device, the internal impedance of the 
cutter should be considerably higher than the external resistance imposed upon 
any cutting medium. This high internal impedance may be achieved either by 



Nov., 1940] 



NEW MOTION PICTURE APPARATUS 



511 



a high order of damping, or by making the stiffness force of the cutter greater 
than the external loading over the useful frequency range. 

With respect to the use of considerable internal damping of the cutter, it should 
be pointed out that such an arrangement has the inherent disadvantage that all 
damping materials change their coefficients of friction considerably with tem- 
perature. Cutters of this kind, therefore, should be used in temperature- 
controlled rooms. On the other hand, a stiffness-controlled cutter will not be 
greatly affected by temperature variations below its resonance point. In a 
high-fidelity cutter, it is probable that a combination of the two methods would 
be desirable. However, for the design of a lower-priced recording instrument, it 




FIG. 3. Feed mechanism. 



is better to depend more upon the stiffness of the cutter than upon the damping, 
since such a cutter will be used under varying temperature conditions. 

Since a high order of internal stiffness is desirable, the Rochelle salt crystal 
lends itself admirably as a motor unit in a cutter. Such a crystal cutter is shown 
in principle in Fig. 4. A four-ply crystal element is held by Koroseal pads. 
This gives not only a very stiff mounting support, but also some damping, which 
reduces the peak at the natural frequency of the cutter. The stylus chuck is 
connected to one end of the crystal element, and because this stylus holder dif- 
fers greatly from the usual stylus mountings, a short explanation may be of 
interest. 

The stylus holder has a V groove, bent in the form of an arc, as shown in Fig. 
4. This permits the stylus to rest upon two points. An important feature of 
this design is that the set-screw is mounted in the cutter housing in such a way 



512 



NEW MOTION PICTURE APPARATUS [J. S. M. p. E. 



that its axis is on the neutral axis of the crystal. Therefore the set-screw does 
not participate in the motion of the stylus, but provides only the third point of 
support for it. This design eliminates any additional inertia inherent in the 
usual stylus mounting. The reason for forming the chuck as described is to 
give the stylus such a support that the overhanging end of the stylus is small. 
Experiments have indicated that some commercial styli have a tendency to 
break up when cutting the higher frequencies. This can be eliminated if the 
stylus is supported as described.